I checked out the existing project source code from SVN to a folder in my system. Then I opened eclipse. Import Project-> Existing Maven Project.
It imported without iss
Check and make sure you have eclipse pointing at a Java JDK directory instead of a Java JRE directory.
I had just installed eclipse and only the JRE was in the settings. I added the JDK path, changed it to the default and clicked on Maven -> Update project. Then the packages appeared in Package Explorer.
The hint that helped me figure this out is that when I tried to use the refactor to rename a class, it wouldn't do it, complaining that it wasn't a JDK.