
You don't need the original CDs . . .
. . unless it's a big name brand (Dell, HP, Gateway, etc. - see below)
What you need is any XP CD of the same type (Home / Pro), preferably SP2 and the license number from the current install (is it on a sticker on the machine?).
First try a repair install. Take "Install" not "R"=Repair at the first offer, then after the system finds the current install take "R" there. Unlike W98 you still need the proper license number.
If that fails, do a full reinstall.
If it is a big name brand than you need a CD from a more or less similar machine of the same brand. You don't need the license number because the number on the machine and the number registered in Windows are both phony - neither one will activate.
[link|http://www.aaxnet.com|AAx]