I don't use Fedora. But basically you need to install rdesktop, which will let you remotely login to XP. It's like XP's remote desktop connection. I think Fedora uses Yum to install packages, so you can probably do yum install rdesktop.
Then run rdesktop, enter the IP address, and you should get a login prompt. If I remember correctly, he can't be logged into the XP machine, and the XP account you use to login must have a password.