That POJ is an oldy moldy blast from the past. Why are you wasting good money on a board that was obsolete before you were born?
Oh, and if the Extreme isn't good for gaming, what would be the best CPU under the given guidelines of the Mobo?
Not sure on the CPU.
But the one thing that does look dodgy is where the ATX plug is in adjacent to the PCI-E port. It would have to be a single slot GPU in my opinion. And i wouldn't go for anything to high spec anyway as that Pentium D (Extreme or not) will bottle-neck most GPU's.
I notice the motherboard is back to front like it is in my Wife's Dell machine. So once fitted in to the case there would be no room for a double sized graphics card anyway. The wife's is a Pentium D as well (Can't remember exact model) but it's at 3GHz with a Nvidia 9500GT which actually runs Counter Strike Source at a pretty stable 80-100 FPS.
I'm thinking putting the MOBO in a bigger case that I have at home in my little "Shop". So, should I go with a Pentium Dual Core? And if I keep it in the case, it won't be a problem because I'm thinking of getting the GTX 640 in a Single slot.... It actually runs better than the 450!
Ahhh good to know you have a spare case to put it in. And on about the CPU. Pentium D's are slightly better than the bog standard P4's but at the cost of more voltage and then more heat of course. Personally i'd just go with a 3GHz Pentium D (No point wasting to much on that system as you're fully aware of. And you also mentioned spending the least amount on it already).
And on about the GTX640. Yes it should run in there fine but as i said before the CPU will bottleneck it. To be honest it shouldn't be to bad and if you can get the GTX640 cheap enough, then why not!
Problem, the GTX 640 is 3.0 x 16.... UGH! My big problem is the power plug like you said.... What can I do?