You might also take a look at the registration system Solution Grove just completed for Museum of Science in Boston courses.mos.org and for an education department within Massachusetts General Hospital. The package handles both registration and creating a collaborative space for the class/event.
Screenshots and features are described here:
http://www.solutiongrove.com/products/registration
The code is in OpenACS CVS, called dotlrn-eccomerece as it ties together dotlrn and eccomerce.
