Depends on how you are getting your variables for passing. If it's coming from a form them you need to make your form a POST form.
If it's comming from a link then you can use frames, or you can use session variables to hide things, or just plain cookies. Unfortunatly this method assumes that you are passing the same information and values everytime.
There is also an article on this site called "Desiging Sites With Search Engines In Mind" or something like that. It talks about how you can build your site to look clean while still getting variables in the url.
