Don't worry about it to much, there are tried and tested techniques for insuring that search engines treat your dynamic pages just the same as static ones.
If you check out my site http://www.explodingnet.com and go to one of the articles you'll notice that the URL is a bit weird: ~/articles/latest/8/
It's the same as ~/articles?section=latest&id=8
There are a few articles on how to do this including a very good one on http://www.sitepoint,com but if you are considering a premade solution just check to see how they handle it.
Good luck
Nick