If you get a WIN7 computer, go 64-bit and put about 8GBs of RAM in it.
Also, consider Microsoft Foundation.
I'm not sure how much 8GB would be of use *in a dedicated Win 7 Pro* machine. If this is a dedicated AC computer, SQL Server Express will use 1GB Max and Windows Processes maybe 1GB max. Even now with iTunes, firefox (500 mb), chrome, and skype. I'm using about 2GB. 500 MB of that 2 GB is from Firefox with 20 tabs open ha. Then again, RAM is pretty cheap nowadays.