Saw this interesting article with the same title here
http://www.searchtools.com/robots/goodurls.html

It starts simple defining dynamic urls and the problems. It then discusses url rewriting and its problems with some links to articles about it.

Finally there are some links on how to do it with PHP. Sadly the greatest thing isn't free called portalpagefilter and it only works with IIS.

http://spider-food.net/dynamic-page-optimization-b.html has some information

And although this is talking about PHP nuke its got a lot of relevant stuff http://mtrad.com/SimpleURL.php

Here is a beginners guide to mod_rewritehttp://www.sitepoint.com/article/910

IF you've got any good ones please tell.

Some more good stuff especially for people that don't have access to mod_rewrite:
http://puzzling.org/computing/help/html/uri

and I got a link to this from that page:
http://www.devarticles.com/art/1/143/ which is a very comprehensive guide.