|Which do you want? And How bad is Windows? And is everything personal backed up elsewhere?|
If windows xp just won't start, but you think it may be ok otherwise, OR you need to try to save files, try a repair install and DON'T delete or format!
If Windows xp is bad AND everything is backed up, AND you have programs and drivers to reinstall, a clean install of windows MIGHT (probably) will bring you back to a near new computer usually problem free. BUT you will need an install CD for windows NOT a recovery CD, that works with a recovery partition on your hard drive to repair windows.
If you cannot repair windows but need to recover files, I believe there are a few ways to boot to a CD (windows install disk or linux CD) and recover files, Just ask, there are others here who can give you more details on this than I can.