I'll give you my totally unbiased opinion....
Instead of a full sized motherboard, take a look at the Travla C137-120 case and a P4 mini-ITX mobo (like an Insight). The case is relatively cheap and comes with a 120 watt DC-DC ATX PSU inside. If you pair that with our CNX-P1900 regulator you will have a 120Watt P4 system equivalent of the Opus, but at a much cheaper price. The P1900 includes a startup/shutdown controller, anti-thump control for your audio amp, and "pulse start" so that you can remotely start your system. You can also power your screen from the P1900 and "over clock" it at 13+ volts for a brighter screen. The P1900 will be available in April and will retail for about $99.
I hope this is helpful info. Good luck! It's a great hobby.