It sounds like there is more at work here than a virus, but with no XP CD recovery will be difficult, if even possible.
You can download and boot with a Knoppix LiveCD and transfer the data across a network, to a computer with a CDRW, or a Pen Drive, or whatever so you should be able to get the info out, unless the info has been encrypted, etc. It would also allow you to see if the hardware is intact. It may not be. In that case the hard drive could be slaved to a working machine and data saved that way.
www.knoppix.com for a free CD download. You have to burn the ISO to a CD with Nero, etc. Don't just copy the file. That doesn't work.
You can test the hard drive with free diagnostics from the manufacturer's site.
http://www.computerhope.com/cgi-bin/yabb/YaBB.cgi?num=1122425778I would also test the RAM. Free download at
www.memtest86.comLet us know what you find out.