Remote Desktop?

First you need to enable remote desktop on Windows XP. Open properties of My Computer and click the remote tab. Also make sure your account has a password.

Next you need to know your home's IP address. The easiest thing there is to use some sort of dynamic DNS service. Use Google to research this.

Finally I am assuming you have some sort of firewall or router at home. You need to forward port 3389 to the home computer. How you do this depends on the router make/model. Check your manual.

I hope this helps!

I use logmein.com. Sign up for a basic account that is free to use. Its really great. All you do is install the remote connection software on your home pc and you can connect to it from anywhere. You can also get a trial if their premium account.