This is a computer case I built up for use in a live situation. The unit has a P4 computer which is setup to run a program called Cantabile. This software aimed at playing live allowing you to have song names with a pile of what it calls rack which contain any arrangement of VST synths and effects.
The reason for building is that a standard pc computer case is reasonably noisy and fragile whereas I think this case would take being beaten around a little more. The fan on the front is the only fan in the unit. The lid is held on with door clips so it's easy to get apart if needed.
I had an old Echo audio Darla card laying around which does a great job as the sound card giving me balanced audio outputs. Of course on top of this is a LCD monitor with keyboard and mouse though the keyboard isn't really necessary for live performance.
I also use this in the studio as my main music software Sonar struggles when playing a softsynth with little latency whereas this computer along with Cantabile is high responsive.