Basically, you are introducing state into a stateless protocol (HTTP). There are really only two ways to do this, keeping state in the client, or keeping state in the server.:

• The most obvious way to keep state in the client is cookies. Others have already mentioned CGI::Cookie. Another generally useful resource is www.cookiecentral.com.
• If you decide to keep state on the server, you'll need an entirely dynamic site that can keep state in GET type urls. (i.e. http://blah.com/page.html?user=joe)

  PHP supports this type of thing with "sessions". If memory serves me right, you'll have to build PHP with the "--trans-sid --enable-track-vars" flags.