I tried to install one of the Express editions recently for a friend (from a download I had done previously), it asked to register for a serial number and I didn't have network on that computer nor I had a serial. That was bit annoying and I wonder if it checks the serial or if you can just use the same serial over and over without checks incase MS pulls the registration site if they haven't already. (Part of the reason I was trying that was so I could do some local C# debugging of some own code I was showing)