Edit: no surpises that Joe said exactly the same thing but faster

You might like to have a look over at maptool - it's also a java app that works as a shared map for people with dice and chat built in.... and macros, and dynamic light and vision and quite a lot more. You can find it over here:

www.rptools.net

The forums are the best documentation. There's a new build out every week or so at the moment and the dev version is now very stable as they are approaching the end of the 1.3 cycle. There's a fair amount of cross-over between these forums and the maptool ones so you'll see some familiar names over there.