do you have an actual copy of xp to reformat with? if you do, try this:
boot to the xp cd
allow setup to run
go through the licenseing agreement and everything
and now you want to do a 'repair installation'.
DO NOT select 'install fresh copy' because that will wipe your drive
doing a repair installation will basically install overtop the existing install. It won't create a dual boot system (unless you select new install, which you don't want.)
this method saved my ass more than once!
go here for a pretty detailed explaination of how this works:
http://www.webtree.ca/windowsxp/repair_xp.htm