I've been working on an HvZ game engine to plug into our Drupal 6.x based website, and it's just about good enough to be released
Video of it in action - http://www.youtube.com/watch?v=SV1sEaEqPBI
The module hooks into the Rules module which in turn allows it to hook into most of the modules made for Drupal. Meaning there are basically endless configurations to what the site could end up being...
While the HvZ module is basically plug and play, getting it to the point in the video is quite a bit of work. This is not meant to be a quick replacement for HvZ Source, but something for schools that need flexibility and have access to hosting.
The module is currently being reviewed for hosting at drupal.org, but for now you can download the files at http://github.com/blaxbb/HvZ-Drupal-module
Our site hasn't launched yet (still waiting on some hosting stuff) but I'll post the link when it's ready