There is a free piece of software known as VNC that allows a remote computer running a VNC “client” to see the screen of and manipulate a computer running the VNC “server”.

It's free and easy to use, once it's set up. But, I can't vouch for the simplicity of setting up the server on a Mac.

Assuming you have Mac OS/X, you can download the server from:

 [[ http://sourceforge.net/projects/osxvnc/ |External Link]]

(Scroll down and click “Download”)

Then, on your Windows box, you can download the VNC client from:

  [[http://www.realvnc.com/download-free.html |External Link]]