Windows 7 - How to change drive letter in XP when dual boot with 7?

In 7 everything is all right.7 is c: and the boot partition is hidden.
But in XP the hidden partition is c: and visible.XP is d:,so some programs use default dir can't work.I tried disk management to change xp to c: but didn't succeed.
Anyway to change the drive letters and hide the 100m partition?
Thanks.

Have you tried Disk Management, right click the partition you want to hide, select Change Drive Letter and Path, click Remove?

Nope,but can I remove the boot partition?(the 100m one)
I just know that I can't change the drive letter of partitions are active or boot..

Yes you can remove the letter from the boot partition.

While in XP, once you remove the C: from the 100MB partition, select Win key +R on the keyboard and type Regedit to enter the registry editor.

Navigate to HKEY_LOCAL_MACHINE\System\MountedDevices. Go down the list and find \DosDevices\D: and change the D: to C: by right clicking on it and selecting rename.

Check to see that no other Dosdevice is set to C:. If it is rename it to some unused letter. This should not be necessary if you removed the C: in disk management.

As always be careful and backup the key by selecting file and export.
Making an error in the registry could make your system unusable.


Edit: Forgot to add - Reboot after drive letter change D: to C:

If you remove the boot partition then your computer won't boot

If you remove the drive letter, it will be hidden.

Thank you for your advices.
I thought it would make the system unbootable.Now I'm gonna try it.
Thanks again.

Report.
I think dual-boot makes things a little bit complicated.
I tried diskmanagement in xp,and it said I couldn't change the drive letter of boot partition or system partition.(the c:\ )
So I follow the mounteddevices thing (kb223188),changed the 100m partition to z:,and then xp partition to c:\ (formerly d:\),and then rebooted.
But it just hangs up at the welcome screen and show "windows xp" but won't logon to desktop.So I have to force power off.
Any idea?

You can NEVER force the drive letter to change on an active system partition. There are thousands of registry entries that need changing. Google would have set you right.

I hope you made a backup image using the great new Windows 7 backup imaging. Takes 20 minutes to image the whole HDD, 20 minutes to reimage it flawlessly.

If not....

You need to boot into your XP disk and run a repair install to recover it's boot. This is not the choice to choose "R" on the first given menu. Proceed as though you are going to install XP until it discovers your installation and asks if you want to install there. Instead choose to have it Repair that same installation. It will replace all of the system files while saving your programs, drivers, settings - everything except activation.

When this completes, you will only have the ability to boot into XP until you 1) use EasyBCD to rediscover the Vista and install its bootloader, or 2) run Startup Repair from the Windows 7 installer (may need to run it twice or more, esp. if it offers it straight away).

Others may have suggestions which are easier but this is how I have recovered from this situation in the past when I tried to change drive letters on a system partition or other times when I have lost a dual boot..

Yeah,thank you,I just made a ghost backup 1 hour ago before I did this.I know it's risky.It can be a final solution.
But even if I made it back to xp and use easybcd to fix the dual boot,the drive letter in xp is still messing,isn't it?
And there is no way to hide the 100m partition in xp?

I believe the solution is to remove the 100mb boot partition and install the bootloader on the XP partition (it is the first one, right?). That should sort the letters out.

Since you are smart enough to have the image backup, you can afford to try it with a fresh reimage if you're adventurous.

I have not done this myself but read many complaints about the 100mb partition in the beta days and how people yanked it out.

You will need a partition manager to delete it, then the method of your choice to restore the boot. I haven't actually done this one, so others should know the best way.

EasyBCD and VIstaBootPro would do it but mine don't boot, so you would need one that does unless you can delete 100mb part. without restarting. That or run the XP repair install to get it up and running so you can use EasyBCD from it.

However, if you end up using Windows 7 startup repair to get it's dual boot back I wonder if it would rewrite the 100mb partition?

Someone will know. Or you'll find out...