If you have two monitors and two computers, but don't want to use two mice and two keyboards, then you should use
Synergy. It will share out a mouse and keyboard from a "host computer" to a "client computer" over a standard network. Just place each monitor next to each other and it's like dual monitors where each monitor has its own computer. It will even transfer your clipboard contents.
There are Windows, Unix, and OSX ports of this program, but the Windows client is the most full featured (followed by the Unix port).