What I've been using for months is UltraVNC. Not only is it a super-powerful VNC, but simple configuration will allow you to use it without installing any software on the client computer.
After you install go to settings and allow connections over ports. (Change from the default to shield against future exploits.)
Open both ports on your router and your done. There will be a little http server running with a java client on your box without any hassle with IIS. Login to your home box in Firefox or IE using http://[your.home.ip]:[httpport] 4900 by default.
As Derren said keeping those ports closed on the router and using a VPN is much more secure, but less doable from a school PC.
