64 bit has a RAM limit but that limit is theoretical at this point. Windows drops the limit to much more realistic number 8GB, 16GB, 128GB depending on your flavor, oddly Mac OS X does not impose such limits and only comes in Consumer and Server.

It's been suggested to get a gaming machine, and I agree with that. Some folks'll grab an HP in the discount isle for $399 and these are problems waiting to happen with integrated components that were lackluster to begin with.

An Intel i7 or AMD, it's up to you. I have an i7-920, the clock speed is deceiving and would appear to be less than it really is but is known for its ability to OC past Intels costing 3x as much, the i7-930 is the CPU that replaced it. I have 12 GB of DDR3 1.6GHz RAM and an Asus mobo with 6 RAM slots to equalize some of the expense. (Note, the new iMac has an option for an i7 Intel and 16GB of RAM, it will run windows 7 64 like a champ and has a 27" LCD that rocks)

Power is a much more serious issue than it was 5 years ago, I'm running a single nVidia GTS 250, two drives, one DVD and fans in a LianLI case and I'm using a 750 Watt Corsair, I think SLI is overkill for Studio but your mileage might vary. ATI or nVidia, just not integrated into the mobo.

In a "what the hell" moment I bought StarCraft 2, installed it and ran it full blast on my system at 1900x1200 with all options cranked. The system didn't so much as hiccup. (I am however getting my butt pwned by the CPU)

my next investment is a Corsair 600 case and a liquid cooling system to further up this system.

This system above works very will with Studio for the most part but Studio does not feel totally optimized for 64 bit at this time. It's fast, but there is plenty of headroom for faster especially when the scenes get busy.

3Delight is very responsive when I render, but it pins the CPU, which is was designed to do.