+1 on the Windows 7 x64. With 4gb of memory you will be much happier using it all
You might want to pick up a Samsung Spinpoint F3 500gb HD to put it on as well. Only $54 at newegg and it will be 3 or 4 times faster than those old 160gb designs even if they are in RAID. I still have my 2 x 160gb Seagate drives from back in the Pentium 4 days. 1 in an external enclosure and 1 in my case as backup.