Are you using SPS or WSS if you are using wss you can add javascript
menu in your defualt themem template or create a new one and for SPS
you may have to do your own webpart or you can also use javascript but
in that case you will have to go to each subarea and change it using
front page read this article for more
http://heathersolomon.com/blog/articles/3500.aspx

Have you tried the Microsoft.SharePoint.Menu from GotDotNet:
www.gotdotnet.com/.../Details.aspx\
6b53-416e-8b06-b8ed84827e97

With FrontPage you can replace the existing menu.

Well, the quicklaunch menu web part is just consumin a list called Menu that
has to exist in the site where you use the web part. Its tree  structure is
achieved by using a named field in the Menu list, called "Group". I believe it
only allows you to have 2 levels of structure.

If you want to get the tree  structure on the quick  launch bar, simple
method is customize ur page, page ur Webpart in the place of left
navigation.

Write tree structure logic in ur Webpart.