When you right-click on My Computer and select properties, there is a rating called the WIndows Experience Index.
You might have to click onthe link to calculate it if it's at one.
I just built a new pc running Vista Ultimate x64 with the following hardware:
Gigabyte p35 based mobo
2 gig ram
8600gts video card
E6850 running at 3gig
I got a 5.6 overall
CPU: 5.6
Memory: 5.9
Graphics: 5.9
Gaming Graphics: 5.9
Primary hdd: 5.7
Post your scores!