One of the most powerful tools that you can use both for SEO and general site management is to utilize mod_rewrite so that all URL are ’search engine’ friendly.
mod_rewrite allows one to control and rewrite URIs. It can turn ugly URIs into meaningful and more attractive URIs that both your readers and search engines can take advantage of.
For some basic information check out the Apache documentation:
http://www.devshed.com/c/a/Apache/Search-Engine-Friendly-URLs-with-mod-rewrite/