X2 4200 is the better choice as it is dual core. Have you considered the new intel Core 2 Duo series? The E6300 or the E6400 would be very nice and are the same price range. Are you building a whole new system? What is the system for? Some things like: price range, uses, preferences for companies really help out with suggestions. Either way good luck and I look forward to helping you more.
The barebone says that it is socket 775, but it says it has a 250w power supply, can i get a higher powered supply from shuttle if the cpu works with it?