Click here, follow the instructions, and read the FAQ :)
Is mucho fun!
You'll probably want a pop-up blocker for the ads. If you don't already have one, a decent one can be found here.
Also, much nifty information can be found here:
I've been playing this pretty much every day since May, and although I haven't really gotten into the RPG aspect of it, I do quite enjoy running around biting people :)