Seriously? You have no idea on motherboard, ram, and processor?
We love to help around here, but if you read any of the new builds, you should have a good idea of what to get.
CPU - E8400 (dual core); Q6600 or another quad core (9450) - your choice - depends on what you are doing with it.
Board - crossfire - X38 or X48 - look at specific features.
RAM - DDR2 800 is a good choice. Choose a good brand - corsair, mushkin, crucial, ocz. Get 2x2GB kit - they are cheap.
Overclock - get another cooler or the water cooling setup.
Do a little research on your own. Figure out what features are important to you/your friend and read through the forums. You should be able to build something very nice w/ that cash.
Come back to us with a list of prospective parts (after you've done some reading and work on your own), and we'll give you some advice and lead you along.
Good luck. Hope to hear back from you with some progress