SSD installed with Windows 7, now to format old HDD

So, I just got a SSD and Windows 7. I plugged everything up, and did the boot install with my Windows 7 disk.

Now, my old 1.5 TB HDD that I want to format (which originally contained Windows Vista), but I'm being told that I cannot from the Disk Management console. More specifically:

"Windows cannot format the system partition on this disk."

I downloaded and installed all the files and software I need to my SSD, and just want to purge everything from my old disk. Suggestions?

No, I didn't unplug it during the install.

Go / Start / "Type" in "CMD" when that showes up right click it and open as "ADMEN" and open// then type (cd C:\ to give you "C:\>" at the end of that type in: your drive you won't to format) like this;;; C:\>format d: and hit enter, then it will tell you that all of your files on your drive will be lost,, do you won't to go ahead?? and that is it. Your drive will be formated.

"" now if you have named that drive then you will have to put that name in the place of (D: or what ever your drive is)

You'll need to write the System boot files to C so that it can boot on its own.

To do this mark C Active: Partition - Mark as Active

Next power down to unplug HD, reboot into BIOS setup to set SSD first to boot in BIOS setup, after DVD drive.

Now boot into DVD System Recovery Options to run Startup Repair - Run 3 Separate Times until WIn7 starts on its own and holds the System Active flags.

You can then plug back in HD, making sure it is not set to boot first in BIOS, copy any files over to SSD that are needed, then to wipe it open an Elevated Command Prompt to run Diskpart Clean Command. Once HD is wiped you can create new partitions as desired in Disk Mgmt: Partition or Volume - Create New