Multi-boot with an XP install disc, if you have one. If all you have is a "restoration disc" that will wipe everything out, I'd say Bittorrent an XP version of the same type as the one included on the restoration disc, eg 'XP Home Edition, Includes Service Pack 1" or "XP Professional Edition, Includes Service Pack 2".. make sure you get the service packs right and that you don't d'l a Business (Corporate) Edition. Then, just use the same key as the one used with the restoration disc; I think it will work. Basically, you're using the exact same Windows XP as on your restoration disc, with the same key; after you install it, you can upgrade to the latest Service Pack.
EDIT: If you don't know how to multi-boot, ask me, I'll walk you through it.