How can I restore my O/S?

I am running XP on my system and decided to partition the hard drive, with Partition Magic, to install Linux. Found out the hard way, it can’t be done. I lost my O/S. Any suggestions on how I can re-install? I have a copy of XP that I made from the new computer but, would like to get the old one back up and running. Hopefully I didn’t fry it.
Rebecca