An installation tarball for Bumblebee (comprising of the PHP code and an install script to generate the SQL files you need to create the MySQL databases) is now available through the SourceForge download mirrors. Installation instructions are also available.
If you want to preview new features of Bumblebee, then the developer snapshots are the safest way to try it out: Sourceforge download page.
Alternatively, if you want to contribute to Bumblebee development, then the CVS sources are the best thing to work with. The latest and greatest from the bleeding edge is available directly by anonymous CVS from sf.net:
cvs -d:pserver:firstname.lastname@example.org:/cvsroot/bumblebeeman checkout bumblebee
or you can browse the cvs repository online.
If you just want to get stuck in and play then that's great, but coordinating our efforts might make more sense as there's a chance that someone is already working on exactly what you want. If you've got something that you'd like to show us, or some ideas you'd like to discuss then contact us with the details. If things look good then they can be included in the next release of Bumblebee and you will go down in history as a contributor to Bumblebee. If you think you will be making lots of contributions to Bumblebee, then we can set you up with write access to the CVS repository.