Actually, I think service pack 4 of 2000 has integrated dual core compliancy.
This has a few answers,
http://www.tek-tips.com/viewthread.c...1273347&page=1
It'll suffer a little in performance, particularly with heavy duty tasking but with small tasks it'll be mostly fine. XP's pretty good if you can live without Vista's shininess.
Do you plan on formatting or are you trying to recover your old Vista?