you can change the drive letter of your boot partition but I wouldn't. Especially if you can boot into xp now.
If you really want to you can try this..
1. you will need to edit the registry so click start run then type regedit
2. the registry editor will open and you will need to browse to first "hkey_local_machine" then to "system" then to "mounted devices"
3. once you click on mounted devices your drives will appear in the main window
4. right click on the drive you want to change and click rename
5. rename it to "\DosDevices\C:"
your drive letter should be C: now. This is assuming that there is no other drive letter using C if there is you will have to change that one first then change the boot drive.
now in order for you to boot into windows you should change this although i'm not sure if it will boot even after you do this.
1. right click "my computer" and go to properties
2 click on advanced
3. there are three options the third is "startup and recovery" click the settiongs icon for that option
4. you will see a line near the top "to edit the startup options file manually, click edit" click edit
5. a file willl open up in a text editor
6. this is your boot options are it should tell you the drive letter that it boots to. If so change it to C:
once you do that it should tell the OS that's want you want to boot into. If you do do this keep your windows cd handy there is a good chance you will need it.
I need a new computer