From your description it sounds like you didn't remove your WinXP partition(s). Chances are WinXP is installed on (hd0,0). You can boot into windows using the following commands at the grub prompt.
If you want to get Fedora Core installed again that will take a bit of searching and reading. Booting from a network is more complicated and you will need a server that has been configured to do this. The Fedora core site mentions Booting from the Network using PXE
, but they don't go into much detail.
If your goal is just to get WinXP running you'll need to uninstall the grub boot loader. Typical way of doing this is using the WinXP CD in rescue mode and giving the command FIXMBR at the console. I don't know how to accomplish that without a floppy or CD. Guess the best place to start looking for that would be the Microsoft site. Sorry I couldn't be more specific with my answer.