I guess it's the pain of using beta software, but boy, trying to figure out what CTP works with what sample application can really be a pain. I recently downloaded Beta 2 of the ASP.NET AJAX Extensions (the extensions formerly known as "Atlas") to see if I could build a neat little site over Thanksgiving vacation (I'm in Ohio right now on slow internet, so that has added to today's frustration...) After downloading Beta 2 and the sample applications, I opened one of the apps, and tried to build it. No dice. It couldn't find the "Microsoft.Web.Preview" assembly. Reading the documentation, I saw that I needed to copy that file into my site. Fine. I browsed to the directory where the assembly is supposed to be--and it's not there. I search online, and confirm--yes, that assembly is part of the AJAX Extensions. But it's not there.
After searching over and over again, I finally came across the answer to my question (on the Microsoft newsgroups!) The assembly "Microsoft.Web.Preview.dll" is not included in Beta 2 installer. To get that assembly (and get any sample app to run), you need to download the November AJAX "futures" CTP. Hmm. OK.
So, if you were searching on the Internet and had the same problem, just download and install the November CTP and you'll be on your way again. Sheesh. I need some turkey.