If you're considering a software based options, look at Microsofts
Remote Desktop Connection Client for Mac to connect your iMac to your PC (I am assuming it is running Windows OS). If you're running linux - vnc server on the pc and a vnc client (Chicken of the VNC) would do the same trick.
Here is a good link for various connectivity options:
http://weblog.bignerdranch.com/?p=14
Hope this helps!
-Ravi