Pretty URLs are fairly simple. Either use mod_rewrite (for Apache servers) or its equivalent on your system to do the complete work, or use it to redirect to a centralized script that reads the URL parameters and shows content based on that parameter.
At work, we have listings like: www.ombe.com/listing/2151404/Uninet-Developer-for-use-in-Ricoh-Aficio-200,-250,-345g
mod_rewrite has this rule:
RewriteRule ^listing/([0-9]+)/?.*$ listing?$1 [NC,L]
"Listing" does something like this:
$product_num = intval($_SERVER['QUERY_STRING']);
Of course there's a LOT more, config and security modules before this point, and error handling for invalid query strings, and so on.