You'll need to build Emacs with DBus support to actually use DBus. On OS X, that's rather unusual, and I can't see what you'd want to use DBus support in Emacs for, given that nothing else uses DBus on OS X.
If you're just after notifications, though, you don't need DBus. In fact, DBus won't give you notifications on OS X.
For notifications on OS X with notify.el, you need Growl. Namely, you must purchase Growl in the AppStore, or build it yourself, and additionally install Growlnotifier from http://growl.info/downloads.