Planning new comp. Ram recommendations plz.

How much RAM does 1 need nowadays? 1 gig?

I'm a huge Corsair otaku. They have the Twins, Valueselects, etc and I do not know the difference between them. Considering I'm getting a Socket 939 CPU which I will OC, what kind of RAM would be sufficient? What speed would I need the RAM to be (considering the 939 lacks FSB) - as high as possible or just DDR-400?

So in brief:
-How much RAM do I need?
-What are the different types of RAM?
-How fast do I need the RAM
-How much will it cost (minimized)?

welcome.. checkout the pqi thread. looks like this is some good ram..