How can I optimize this site?

I’ve been using www.websiteoptimization.com to optimize my site but I recently moved to CSS and now every other analysis is a Caution or Warning. What can I do to optimize this site:

http://www.u-stu.com/index032.html

Using the same optimization site, www.yahoo.com checks out 100%. Why does it show only 3 images on Yahoo when there’s obviously a lot more? To let you know what’s over my head, I know quite a bit of html, intermediate CSS, and pretty much nothing else. Thanks.