I'm running Protools 8 M-Powered using an i7-930 on a X58 Sabertooth board, 6GB of Kingston HyperX and Win 7 64-bit. I just built the PC a month ago. The processor is extremely effective at processing all the RTAS/VI I throw at it and asks for more. Protools uses all 8 threads. I'm pretty satisfied with the setup so far.
Also, the device you use to record has a lot to do with what kind of latency you'll be dealing with. There are cards out there that offer 0 latency (or as close as possible). I'm using a Fast-track Pro USB for the input and connection to my monitors (Rokit 6s). It's a good unit for recording 1 or 2 tracks at a time. It's not a 0 latency device, and there are better devices out there, but this thing is great for my home studio.
Additionally, a good rule to follow is use 7200 speed SATA 2 or 3 disks and run the recording app from one disk and record your data to another. I use a WD blue drive for my app and a WD Black for my record drive.
Edit.. My God is OP's post old. Is OP still with us? What did OP decide?
The most important thing you have to look out for is Windows 7 64 bit compatibility for the device drivers. Ole Fonzarelli above me uses a fast track which is great as Maudio are bang up to date with Win 7 64 rev 1 drivers.
You also need your software daw to support 64 bit, otherwise it wont take advantage of your ram etc.
Raid 0 configs are best for sound/video recording for the speed, but you have to set up a backup since one drive fails, you lose everything. I use USB3 backup as it is nice and fast.
So 8 gig, raid 0, phenom, 64 bit drivers and 64 bit software daw and you will be laughing. Note also VST plugs come in 32 and 64 bit flavors.
I had to return Lexicon and mackie USB recording devices due to the drivers nto working on Win 7. They claim they do, but they dont.
One thing, though... RAID 0 setups are unsupported in ProTools 8. They don't appear to be explicitly supported in ProTools9. I'd suggest you check with the audio editing/production software vendor on disk setups.
I tried to run ProTools 8 M-powered in a RAID 0 against the hardware recommendation and it was altogether glitchy when recording.
Again, check with the software vendor for recommendations on disk setups.