I would like to replace XP operating system, vista, but not C disk format. How …

a loaded WINPE, restart the computer to enter WINPE can set the format c immediately
This is because the system installed You installed is higher than the level of xp, and then installed xp format, so difficult format, you can try to look at the ghost version of xp, direct coverage, you can, you can re-loading your favorite version of xp into the system After the disc format c, is not in the Control Panel to uninstall, use the XP installation CD-ROM drive to start with, prompted by the installation disk format C, and then install XP.