I haven't heard of anything like playing a tone when there's a new post, but you could easily enough set that up with a javascript I guess.
Take a look at phpBB, I use it on my site. It's very similar in layout to vBulletin, but *very* fast, and also free

.
www.phpBB.com
There are alot of addons for it at
http://hacksphpbb.sourceforge.net
It'll run on Windows IIS or Apache, only requirements are PHP and a MySQL database.