Re: Computer - is this a good build? - what motherboard should i use?
I have two issues with your build. Firstly, I wouldn't recommend using a P4 at the moment. Intel has just anounced their new chip which will be with us next year and looks like it will be comfortably the best chip available. As it is, I would build around a cheap AMD 64 chip for now before upgrading later- a good motherboard would be anything from the Asus A8N line as they're cheap and perform well. AMD generally perform better then P4's.
My other issue is your graphics card, as the 6600gt is getting on and will struggle a lot when games such as F.E.A.R. come out. If you are interested in gaming, I would suggest getting some cheaper ram (not neccessarily less) and spending the excess on a 7800gt.
Lastly, if you still want to get the P4 (they are still the best at video encoding), make sure you get a board based around the 945 or 955 chip- they offer better performance and upgradability. Older 915 motherboards are cheaper but not as good.
Asus P5W DH Deluxe/ Corsair 4GB DDR2 XMS2 Dominator PC2-8888C4/ Gainward BLISS GeForce 8800 GTX 768MB + 'secret'/ Intel Core 2 Quadro Extreme Edition QX6700 @ 3.6ghz/ 4x Western Digital Raptor X 150GB/ Swiftech H20-220 Apex Ultra+ watercooling