HDD advice

Just connect the hard drive up - even if it shows in the boot menu your latest version should be first - go into w7 go to diskmangement and quick format the drive - if it wont let you, delete the volume and recreate it, and quick format it - if you delete the volume and recreate it you wont have to remove it from boot it does that automatically - otherwise type msconfig.exe in search, and select boot then delete the w7 entry.

Another point I overlooked was did you install the w7 to the new drive while you still had the old one in the PC because thats about the only way it will be on the boot menu so there may not have to remove it from the boot menu.

You should read the following also about adding drives to the PC -

Move Disks to Another Computer[This topic is pre-release documentation and is subject to change in future releases. Blank topics are included as placeholders.]

This section describes the steps to take and considerations associated with moving disks to another computer. You might want to print this procedure or write down the steps before attempting to move disks from one computer to another.
Backup Operator or Administrator is the minimum membership required to perform these steps.
Verify volume health
Use Disk Management to make sure the status of the volumes on the disks is Healthy. If the status is not Healthy, you should repair the volumes before you move the disks.
To verify the volume status, check the Status column in the Volume List view or under the volume size and file system information in the Graphical view.
Uninstall the disks
Uninstall the disks you want to move using Device Manager.
To uninstall disks
Open Device Manager in Computer Management.
In the device list, double-click Disk drives.
Right-click the disks you want to uninstall, and then click Uninstall.
In the Confirm Device Removal dialog box, click OK.
Remove dynamic disks
If the disks you want to move are dynamic disks, in Disk Management, right-click the disks that you want to move, and then click Remove Disk.
After having removed dynamic disks or if you are moving basic disks, you can now physically disconnect them. If the disks are external, you can now unplug them from the computer. If they are internal, turn off the computer, and then physically remove the disks.
Install disks in the new computer
If the disks are external, plug them into the computer. If the disks are internal, make sure the computer is turned off and then physically install the disks in that computer.
Start the computer that contains the disks you moved and follow the instructions on the Found New Hardware dialog box.
Detect new disks
On the new computer, open Disk Management. Click Action and then click Rescan Disks. Right-click any disk marked Foreign, click Import Foreign Disks, and then follow the instructions on your screen.
Additional considerations
When moved to another computer, basic volumes receive the next available drive letter on that computer. Dynamic volumes retain the drive letter they had on the previous computer. If a dynamic volume did not have a drive letter on the previous computer, it does not receive a drive letter when moved to another computer. If the drive letter is already used on the computer where they are moved, the volume receives the next available drive letter. If an administrator has used the mountvol /n or the diskpart automount commands to prevent new volumes from being added to the system, volumes moved from another computer are prevented from being mounted and from receiving a drive letter. To use the volume, you must manually mount the volume and assign it a drive letter using Disk Management or the DiskPart and mountvol commands.

If you are moving spanned, striped, mirrored, or RAID-5 volumes, it is highly recommended that you move all disks containing the volume together. Otherwise, the volumes on the disks cannot be brought online and will not be accessible except to delete them.

You can move multiple disks from different computers to a computer by installing the disks, opening Disk Management, right-clicking any of the new disks, and then clicking Import Foreign Disks. When importing multiple disks from different computers, always import all of the disks from one computer at a time. For example, if you want to move disks from two computers, import disks from the first computer and then import disks from the second computer.

Disk Management describes the condition of the volumes on the disks before they are imported. Review this information carefully. If there are any problems, this will tell you what will happen to each volume on these disks once the disks have been imported.

If you move a GUID partition table disk containing the Windows operating system to an x86-based or x64-based computer, you can access the data, but you cannot boot from that operating system.

First download your motherboard manual at:

http://america.gigabyte.com.tw/FileL...3l(us3l)_e.pdf

The thing to do is to boot from the new disk, with the old one attached. Just make sure in the bios/cmos setup that the machine knows to boot from the new hard disk. If you do this, it won't even know that win7 is still on the old disk.

Once in windows, click on My Computer and you will see the old disk listed AFTER the new disk and you'll see that the new disk has a C and D drive and that for the old disk, the old C and D drives have new names, like E and F. You can then go to start > run > compmgmt.msc (press enter) > disk management and do whatever you want to your old disk, such as format it or delete partitions, whatever.

It is all dependant on making sure that your computer is set to boot from the new disk. Press the delete key during startup to enter bios (page 34 of link) , then once in bios select "advanced features" (page 35), then set your boot order (page 46)

I think the 500w psu should be more than adequate, dont worry about the drives they will be assigned - you can do it in diskmanagement or use the W7 DVD - my first choice would be diskmanagement as its less time consuming. If you delete the partitions (volumes) or see if it will let it format the W7 partition see below - I've had some problems here with previous OS'S when you attempt to erase them by formatting the partition even when they are on a different hard drive - sometimes it wont let you but it will let you delete the volume and recreate.

Create and format a hard disk partition
[This content is preliminary and subject to change.]
To create a partition or volume (the two terms are often used interchangeably) on a hard disk, you must be logged in as an administrator, and there must be either unallocated disk space or free space within an extended partition on the hard disk.
If there is no unallocated disk space, you can create some by shrinking an existing partition, deleting a partition, or by using a third-party partitioning program. For more information, see Can I repartition my hard disk?
For information about reformatting a hard disk, see Formatting disks and drives: frequently asked questions.
To create and format a new partition (volume)
Click to open Computer Management. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
In the left pane, under Storage, click Disk Management.
Right-click an unallocated region on your hard disk, and then click New Simple Volume.
In the New Simple Volume Wizard, click Next.
Type the size of the volume you want to create in megabytes (MB) or accept the maximum default size, and then click Next.
Accept the default drive letter or choose a different drive letter to identify the partition, and then click Next.
In the Format Partition dialog box, do one of the following:
If you don't want to format the volume right now, click Do not format this volume, and then click Next.
To format the volume with the default settings, click Next.
Review your choices, and then click Finish.
Note
When you create new partitions on a basic disk, the first three will be formatted as primary partitions. Beginning with the fourth, each one will be configured as a logical drive within an extended partition.
To format an existing partition (volume)
Warning
Formatting a volume will destroy any data on the partition. Be sure to back up any data you want to save before you begin.
Click to open Computer Management. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
In the left pane, under Storage, click Disk Management.
Right-click the volume that you want to format, and then click Format.
To format the volume with the default settings, in the Format dialog box, click OK, and then click OK again.
Notes
You cannot format a disk or partition that is currently in use, including the partition that contains Windows.
The Perform a quick format option will create a new file table, but will not fully overwrite or erase the volume. A quick format is much faster than a normal format, which fully erases any existing data on the volume.