My colleague Jason has posted a great entry (with a video) on how to determine what version(s?) of SQL Server you have running, at
What’s especially nice about the posting is that it combines together in one place all the different ways of determining the version number. This information is available in the official documentation, but is scattered in separate places, so it is a real service to have it all brought together. Plus it links to a listing that translates the version number into the name by which it is commonly known.
Highly recomended, enjoy!