Depends on 2 things
1. Is the CD Bootable? 99% of the time yes they are, but it depends ... make sure before you format
2. Is your PC new enough to support booting to CD? I'm gonna guess yes, but again check before formatting...
Your safest bet would be to format from within XP's setup so you KNOW you can get into the setup before formatting
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Make sure you have any necessary drivers.. primarily for odd IDE controllers... this is the only place I've gotten stuck on the setup (Abit BE6-II has a HPT 366 controller that for some bizarre reason MS has never included teh drivers in Win2k or XP's setup)