I know the IP address of my iMac and I have been able to ssh into the computer successfully, but I want to be able to control the desktop remotely from my Windows machine as well. How do I enable my iMac to do this? Is there a special program I need to use on my Windows 7 machine to do control the desktop remotely?
You can use VNC to remotely control your Mac. There's instructions around here to turn on the built-in OS X VNC server (it's pretty straightforward), and a Windows VNC viewer (I linked to a Google search because I don't know a particular good viewer for Windows because I don't use VNC on Windows).
Your best option is to use LogMeIn. It allows you to set different resolutions, you can perform Mac gestures, and it uses the least bandwidth of any remote control app I have ever used (about 10-15Kbps for a 1280x720 screen). It is cross platform too.
You create a LogMeIn account and you can either use the Windows client or the web-based client.
Look into TeamViewer. It has a mode to do just just that.