please help, I recently tried to install xp home on c drive as i was having some probs but instead of overwriting old copy it put another copy on so i now have xp home twice on same drive i have tried to delete old copy with no joy as it says i need to reinstall some files, i cant even seem to get an option to format the drive so i can start again. my pc is now constantly crashing about 4 times a day now

If you have a floppy drive on your computer, you can format and partition the drive using a Win98 boot disk. [http://freepctech.com/pc/002/files010.shtml]
Be sure to select CDrom support from the initial menu, so that you can go to the WinXP disk to install the operating system.
Also be sure to backup your data before starting, because formatting removes everything [but you already knew that :)]
If you don't have a floppy drive, try choosing a repair install for the old XP from the install CD. Once it is repaired, you should be able to remove one of the two identical copies.

Have you tried setting your bios to boot from your CD first? Then it will reinstall XP and give you the option of formatting first. but, like dlwolff0 said, back up your info first.  ;D