While we are still in the Beta phase of phpGroupWare, you may want to track the CVS copy as closely as possible. The released versions are more stable, but often contain bugs that have been fixed in the CVS version.
The downloads section on the site contains links to the most recent releases, and several mirror sites for the releases.
If you have never used CVS, you may want to read through the doucmentation found at www.cvshome.org . The CVS pages for the core and apps projects can be found at phpGroupWare Core CVS , and phpGroupWare Apps CVS. Follow the directions for Anonymous CVS access and you should have the most recent development copy of phpGroupWare in no time.