There's a quick post on the bla.st blog about a handy method to create "pretty URLs" for your website without changing your code (much). With this example, it's all about Apache and mod_rewrite.
For our bla.st project, we decided to put all URLs through a single PHP script, and process them there. The advantage is then we can do what ever we want with the URLs.
They provide the settings and directives that you'll need to drop into Apache and what they're doing so you can customize them to your site. There's even a brief PHP example at the end showing how to get the information from the URL and into a usable form.