Ok your running a Intel CPU based on FSB so it doesnt really matter. The higher frequency RAM may give a little better performance but what you need is size, 2x2gig or 4x2gig. The huge cache on intels current CPUs negates a lot of the performance of the RAM. AMDs design and Intels next design wont use the FSB so they will depend more on RAM speed, ie: DDR3. Four gigs of DDR2 800 should be fine for you and be a bit cheaper then 1066 but there may be a little better performance with the faster RAM. I'm talking like 1-2% but it may be more, you should check some of the articles on Toms and other sites that compare this issue.