Looking for answers to using ZB3.1 on your new computer?
Place comments here. 
“Windows XP Professional x64 Edition is designed for you. With its 64-bit processor, Windows XP Professional x64 Edition gives you access to greater amounts of memory while continuing to support 32-bit applications.”
Does Win XP64 actually use Intel Core 2 Quad Q9400
Win Vista Home Premium 64-bit or Win XP-64?
For question 1: Yes.
For question 2: It’s a matter of personal preference. As a general rule, though, you will get better driver support from Microsoft moving forward with Vista than XP.
FYI,
Intel i7 920 2.66 GHz
Asus P6T Deluxe MB
SAPPHIRE 100251SR Radeon HD 4870 X2 2GB 512-bit (256-bit x 2) GDDR5
CORSAIR XMS3 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Triple Channel Kit
Vista Ultimate 64 SP1 (I believe non-Ultimate is just as good for ZB purposes)
All the other stuff you generally need to build a new system, including a 28" flatscreen. 
NOT overclocked or specially tweaked, yet, and it is currently second by a hair only to an i7 940 or 960 over on the ZB Benchmark thread. Total cost was only a bit over $2500, and could have been under $1700 if I’d used DDR2 mem, cheaper MB, and a single-GPU video card, and not bought a 28" flatscreen to go with it.
ZB3.1 runs like a dream so far, as does Fallout 3, Mass Effect, and Company of Heroes. I plan to put PS CS4, SolidWorks 2009, and XSI on it soon.