XHTML 1.1 + php sessions = :(

Hi there guys... First time caller here ;). I'm currently developing a content management system. One of it's features is that it's going to be completely standards compliant (XHTML 1.1). I'm having some troubles however, and they come in the form of sessions. When I use session_start(), it throws the PHPSESSID into the URL of all of my links and form actions and what not. This is a problem because in my forms it throws in a hidden input, which doesn't validate right, plus they don't use & insteand of just &. Is there any way to stop a session from being passed through the URL?