Win-7: Pro or Enterprise, x86 or x64?

Hi - i'm about to install P6 on two MBP 2009 with 2GB RAM and 160GB hard drives, in order to run a few games, IE8, and CorelDraw. I have the option of choosing Win-XP, Win-7 Pro or Enterprise, 32 bit or 64 bit. I've read a lot of threads about the performance of the different versions of Windows, but I can't find anything about the resource (RAM and disk) utilization.

Which version of Win-XP or Win-7 will need the least RAM to run effectively, and which version of Win-XP or Win-7 will consume the least disk space? How much more RAM and disk would I need to use to get better performance, and would the performance be that much better?

I also plan to install P6 to run a few Windows programs on an MBA ultimate (2GHz, 4GB, 256GB SSD). Which Win-XP or Win-7 should I run on that system, given it's greater RAM and SSD?

Thank you all very much for helping me out.