I found this lovely little script this morning and have been playing with it ever since - it's dead simple and works a treat

http://tvcnet.com/php/treemenu/

Examples of it in use (both mine):

http://www.skunkeh.uklinux.net/sp/
http://www.skunkeh.uklinux.net/tree/

The first one is a tree of the forum structure of this site - very useful if you check a lot of forums on here at once and want to skip between them quickly.

Just thought I'd share that with you all as it's a very nicely written script