Here’s a good article on how to maintain back and forward browser history in Ajax applications.

“While Ajax and Web 2.0 are all the rage at the moment one of the most frequent criticisms of Ajax is the lack of the browsers back and forward history functions when using Ajax powered applications. There have been a few attempts at fixing this problem with variable degrees of success. It has to be stated though that no technique I investigated fitted the needs of this site. Part of the difficulty here is that this site is essentially a multi-application site, where multiple blog applications are appearing to the client as one application.”
Link: Ajax History: It’s in a Name - DHTML Nirvana