The Apache Rewrite Engine is your friend.

http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html

In your .htaccess file, you can specify re-write rules that will convert the url to whatever you want it to look like. With this, you can "encode" all the variables info into what looks like a normal url, then "decode" you own code if it's resubmitted.

Another useful page on this specifically:

http://www.devshed.com/c/a/Apache/Search-Engine-Friendly-URLs-with-mod-rewrite/