A new version of Bgui is way overdue, so here it is. Bgui 0.07 brings quite a few changes including ImageButtons and memory leak fixes. It will also work for newer versions of Blender (such as 2.61). For more details on the changes, take a look at the changelog.
You can grab the new version from here.
- Blender 2.5+ (2.61 is fine)
There is also a Getting Started guide in the wiki.