What's the setting? College campus? Church? Youth organization? The scale can make a big difference - if you've got a large group of people you can organize elaborate missions with objectives to accomplish, whereas if 30 people is all you have you might want to scale it down to just a basic one-day event of tag.
I was the admin of one of Ball State University's HvZ games, and I still have this FAQ I made to promote the game on my hard drive. I thought I had the rule set we used, too, but I guess not, which is a bummer because BSU HvZ rules are still based on the rule set my mod staff and I drafted. They may have been a bit much for a pickup game though, since BSU games normally have about 150-200 people playing.
The basics are pretty simple. You start out with a zombie or two, and everyone else in the game is a human. Humans have nerf guns or clean, balled up socks. If a zombie tags a human, the human becomes a zombie. If the human shoots a zombie, that zombie is "stunned" and is inactive for a predetermined amount of time. (In the FAQ I say it's usually 15 minutes, but that's way too long for a game of 30 people. I'd go with maybe 2-3 minutes.) There should be some kind of marker system to know who is who - we used bright green bandanas which if worn on the arm indicated human and if worn on the head indicated zombie. From there, it's all up to how creative you and the people playing the game can get with it.
This is an excellent idea! I know there's a similar one someone has done where they have translated the entire book in Starcraft terms. My suite mate is a big fan and showed it to me, needless to say it was very amusing but, at the same time, had a lot to say about the game's strategy. Anyways checking that out might help you along in this. I certainly know I and a number of my players would be willing to read an HvZ version of The Art of War!
My school uses http://www.HvZHub.com/ which was meant as a direct replacement for HvZSource. Beware though, that it doesn't support some of the more complex game mechanics such as antidotes.
They also just released a mobile app (literally today at like 1pm) for the site.
I made a HvZ server for Minecraft Classic a long time ago. There were already zombie tag servers but I tried to make it more HvZ-like.