With Windows 7 coming up to readily being available you might want to be aware of the memory limits of the different versions. Incidently, my PPBM benchmarking for Premiere shows it is faster than XP and Vista 64
Here are the upper RAM limits for the different editions of Windows 7:
* Starter: 8GB
* Home Basic: 8GB
* Home Premium: 16GB
* Professional: 192GB
* Enterprise: 192GB
* Ultimate: 192GB .
You may want to stay away from the two low end versions especially if and when Adobe really goes 64-bit, but without a doubt you do want to install the 64--bit version of the OS.