I finally got this great application working. Synergy2 allows you to use one mouse and keyboard across multiple computers over TCP/IP no KVM hardware required. One computer acts as a server with the keyboard and mouse attached, and the others as clients. By moving the cursor to the edge of the screen it moves the control across to the next computer. Very handy and much cheaper than a KVM as its free! What makes it really killer for me is that is cross-platform, meaning I can use my mac to control the PC-server on the network, great.
Synergy2 can be found at http://synergy2.sourceforge.net/
If you are using a Mac I ighly reccomend QuickSynergy
it makes the set-up process much much less painful.