Sorry, can't tell you how to restore XP, but I can tell you how to get your un-backed-up files off the disc so you can do a clean re-install.
Get a Linux "live" CD or DVD -- they come on magazine covers at 5 to 7 quid. It will run entirely from the CD/DVD drive, but can mount the data part of the XP disc read-only and a USB stick read/write. Get what you need onto the stick and then go back to your XP installation disks and start from scratch.
If you don't have the XP disks you could try putting Linux onto the EEE notebook. Try Google for instructions, it's not quite as straight-forward as a normal PC, but is definitely do-able.
'b