Then this is what you want. Input Director. With Input Director, you can control several Windows computers with one keyboard and one mouse without the need for a KVM! This works by communicating over your local home network to the networked machines, allowing you to smoothly move your mouse and keyboard commands to the desired machine seamlessly and without lag issues. Simply slide your cursor off screen, and voila! you're on the other machine(s) issuing commands from the same keyboard and mouse you started with.
I use this program at work where we have 6 computers all networked, each with 2 monitors attached to them, and Input Director works like a champ.
http://www.inputdirector.com/Have a Windows machine and a MAC? or Ubuntu or Linux that you'd like to rid the keyboard and mouse of? Then use this cross-platform alternative !
http://synergy-foss.org/