Build Suggestions for Quad core,maybe...

[worshipme]

Are my parts "overclockable"?

The 9950 is pretty overclockable, yes. 3GHz+ is easily possible.

What about my ram, should i run 2x1gbs now, and upgrade another 2x1gbs later on, for a total of 4?

DDR2 is so cheap now, I would just run 2x2GB now, and you can leave the other two slots empty for future upgrade. Make it 1066 to make use of the Phenoms IMC.

Can i mix brands but as long as its pc2-6400?

You can mix brands. Just make sure they have the same frequency and latency specs.

I read some motherboards need have to be running on a 64bit O.S

You don't "need" to run a 64 bit OS, but I would recommend it. A 32 bit OS can only address 4GB RAM -(that's supposed to be a minus ) your graphics memory. A 64 bit OS can address as much RAM as you could ever stuff in your motherboard.

 

[solitary1]

you might have just convinced me to go AMD. Is the difference between 800 and 1066 significant?
is that the mobo i want to go with? are their other alternatives?