Enable the ssh daemon on your Linux box and have it load automatically on boot. This will allow you to always be able to log in to it. An excellent Windows ssh client is
PuTTY - free and also feature packed.
If you want to have a lot of fun, install
Cygwin on your XP box - don't forget the XFree86 part - and enable X11 forwarding in the sshd_config on your Linux server. Then you can log in using
ssh -X username@hostname (where username is your Linux username and hostname the name of the Linux box) and start X applications that will show on your Windows desktop.
Håkan