For those of you who read the previous post you will have noticed some of my questions were answered by helpful commenters.
The first thing that was mentioned is that you can install as many of the express versions as you wish. What you really give up here is the ability to have just one Visual Studio environment that looks the same for all of your projects. For the moment I can live with that.
So I installed the Web Edition and found a couple of surprising items. The toolbox actually included AJAX Extensions by default. There is still a lot more to investigate. Look for more tidbits in upcoming weeks.