My old hd broke and I installed a new one, copied all recoverable files from the old hd and then removed the faulty disk. Now the only hd I have has the drive letter F:, though I prefer C:. The CD drives are D: and E:, and it's hard getting used to the odd position of the hard disk in Explorer tree.

Is it possible to change the letter without messing everything up? Disk Management obviously can't change the boot volume disk letter.

If Disk Management can't change it do you think the Registry could change every entries that refer to the boot drive letter? Nope! You can only start over with fresh reinstal.

i_XpUser

Make sure you back up your hard drive. Note that changes in the system drive, may (more like will) break applications.

KB Article:
http://support.microsoft.com/?kbid=223188

Change the System/Boot Drive Letter
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.1. Make a full system backup of the computer and system state.
2. Log on as an Administrator.
3. Start Regedt32.exe.
4. Go to the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
5. Click MountedDevices.
6. On the Security menu, click Permissions.
7. Verify that Administrators have full control. Change this back when you are finished with these steps.
8. Quit Regedt32.exe, and then start Regedit.exe.
9. Locate the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
10. Find the drive letter you want to change to (new). Look for "\DosDevices\C:".
11. Right-click \DosDevices\C:, and then click Rename.

Note You must use Regedit instead of Regedt32 to rename this registry key.
12. Rename it to an unused drive letter "\DosDevices\Z:".

This frees up drive letter C.
13. Find the drive letter you want changed. Look for "\DosDevices\D:".
14. Right-click \DosDevices\D:, and then click Rename.
15. Rename it to the appropriate (new) drive letter "\DosDevices\C:".
16. Click the value for \DosDevices\Z:, click Rename, and then name it back to "\DosDevices\D:".
17. Quit Regedit, and then start Regedt32.
18. Change the permissions back to the previous setting for Administrators (this should probably be Read Only).
19. Restart the computer.

Good Luck!