I do have another suggestion though. Check out the Processors section of the forum. Words are out that prices will be dropping on dual cores in the next month or so, and may be a better investment than to get a single core, budget processor like the 3500+
(I have it, and its a great processor, but in the next month, dual core will surpass this valued processor)
So I'd check out that
I'd think about getting 2x 512mb sticks, that are Dual Channel Compatable. You should get a performance boost from doing this, over using just one stick. They usually come in pairs, and cost about the same as a single chip.
I don't know too much about these to specifiy, but 550 Watts should be plenty!
If you decided to change the processor, this would probably have to change also.
Wait a second... aren't you getting a new motherboard? So you got a new case too? I'm utterly confused... not that I'd be helpful anyway. I'm probably the most inquisitive, yet least helpful member in this entire community.