I recently had the problem to understand which edition (standard/developer) was installed on an old machine. This sounds like a pretty straightforward thing to do - and it is indeed IF you know you need to run the following query:
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')
You'd imagine you could figure this out looking at the 'about' information in enterprise manager (as in SQL2005 in SQL Management Studio) but that doesn't seem to be the case. I couldn't find any other solution.
Mysteries of MS faith.