Many of your school systems, and maybe even you, use some type of remote desktop viewer. School systems use it to solve technical issues remotely. Families use it to help them less than savvy parents and other family members. The main product out there is RealVNC. We use it at my 9-5, and it works beautifully. At $30 each for the personal edition, though, it can get quite expensive.
Enter TightVNC. TightVNC, licensed under the GPU GPL License, is free. Yes, free as in beer. You can *buy* the source code, but if you just need a VNC client, you are good to go with the free version available here: http://www.tightvnc.com/download.php That will allow you to put the client on your Windows XP, Vista, and 7 hosts.
A word of caution though…Tight VNC (or any VNC client) on your home or school network is pretty secure. When you introduce using it over the internet, you risk security risks. They currently are working on a more secure way to tunnel to external networks, but use it at your own risk now. If you really must use it, look into OpenSSH, something we will review here soon.