Peter Provost picked up on my security note about Enterprise Library 2005 that you must install it to another location than Program Files for developing as a non-administrator (i.e. using a limited user account).
He also mentioned that some of the NUnit tests will not work unless you are testing as an administrator. This is very unfortunate, and Peter mentions he wished they had dealt with those exceptions appropriately. He offers some solutions, and they are good, but I hope this will be a clear call to the team for future versions to consider all aspects of developing as a non-administrator, including development as well as all unit tests.