Either way, Teleport (I think is the name of the software) lets you use one keyboard/mouse on more than one Mac, just move to the top right/left corner of your screen, and keep it there for more than x Seconds, and it'll switch to the other Mac
Here's the direct link to the teleport software. Both computers of course must be on the same network for the protocol to work correctly. Once the software is installed, you will find it in the Other section of System Preferences. Within is where you can enable the service, and also select the configuration settings for sharing the keyboard/mouse between the two Macs.