i just got approvad for adsense and i need to ask how many ad units are allowed per page in total. please see my blog and advice if i done it correctly or not http://your-health-matter.blogspot.com/2009/08/reason-for-fat-in-our-body.html
I think they are OK. The only think I suggest is to change the background colors of the ads to fit the background color of your site's background.
You can't add more ad units. You have 3 ad units currently. Rectangle banner = ad unit. You can add 2 more Link units.