The Tech Daily

Please check that the two computers you wish to share one keyboard and mouse between are networked, as this is the only requirement.

Input Director

Input Director is a windows-exclusive program that allows you to control more than one computer without using more than one keyboard and mouse. With input director, you simply control both computers with the keyboard and mouse, and press a certain hotkey to change which computer you would like to control.

You can either use the hotkey method, or just move the cursor off the screen, and it will appear on the other computer, allowing you to use the keyboard for that one instead.
please note that the only systems that currently support Input Director are Windows 2000(SP4), Windows XP

(SP2) or Windows Vista. And the computers you wish to control simultaneously must be networked.

Download : Input Director
Source: Online Tech Tips