Create Variable from URL Data

I am looking for a way to take info from a URL and turn it into a variable I can use in a PHP MySQL query. The URL data is not a result of a form submission etc…

Basically, I am designing a site for someone where people who sign up on the site can have two types of accounts - basic and platinum - and each person who signs up gets their own “storefront” to re-sell e-books and what the storefront offers is dependent upon the account type.

The storefront pages will be located at a URL that has the owner’s id name in the URL (i.e. http:\\\joegreen). I want to find a way to turn the owner id name (or “joegreen”) into a variable so that when someone visits that storefront a PHP MySQL query can be run before it loads to determine the account type of the store owner and display the correct storefront for that account type.

Is this possible? or is there another way that I could do this?

google for [google]mod_rewrite[/google]
you can change parts of the URL into $_GET vars with that.
and than read these vars and show the correct page