You can also make different versions of your site and use some code to redirect your visitor based on their resolution. Works pretty good on smaller sites....frames can be a pain though.
Check out
http://www.echoecho.com/toolscreenre...onredirect.htm for the code and if you want to see what your site looks like at different resolutions go to
http://www.echoecho.com/toolresizer.htm and enter the url.