The treemenu should be displayed in the left div, but it doesn't.
If you only execute the tree menu, it works:
The main use of AJAX is to pull content generated from a server-side script and put that content into your webpage without refreshing it. Webpasties has a very good base tutorial. So in the webpasties tutorial, the server-side script just generates the city and state of the zipcode entered. This information is then dissected by the client and placed in the right areas.
I hope this made sense and I understood what you are trying to do correctly. I didn't get too far into your code, but this should help I'd think.