Heres the deal. For years I had Win2000 on my machine. I finally decided to move to XP, but wanted to dual boot to make sure I wouldn't have any issues. I have 3 harddrives on this machine, but we don't need to worry about the two IDE ones. My main SATA drive (250GB Seagate 7200.10) is partitioned 4 times. 30GB C, 50GB E, 50GB F, and 100GB G. Win2000 was on the C drive, the test install of XP went on G.
I dual booted for several days, and decided I wouldn't have any issues with XP. I went ahead and put my CD back in the drive, and told it to upgrade my win2000 build. Heres the problem, I can't remember if I ever deleted the copy on G. I don't have the option to boot to it anymore, so at the very least at some point I removed that option from my boot.ini file. I do have a documents & settings folder, a program folder, and a windows folder on the G drive. In 98% sure that the copy of windows I'm using is on C, but is there any way to know for sure? I'd like to regain the 2GBs of space that these folders are taking up.
Just check your boot.ini file on the root of c: drive. If your default is showing your first partition, you're good. If not, change it to reflect the values of your first partition, c: drive and reboot.
If it's still set as dual boot, you'll see two entries under the operating system section. The first should be your c: drive install, the second your g: drive.