I have an iogear usb version that works great. has audio also and was only 90$ canadian (75$ us).
it works very simple. just hold f12 down for like 1 - 1.5 sec then capslock light flashes till you make a system choice which is done by pressing 1 or 2+enter. what I like most about it is that it keeps the screen position and everything else just the way I want it on both systems.