I know I probably shouldn't be this excited, but I've just installed VSTS B3 into a single VPC image, and it worked first time!!
Still a couple of funnies, reports don't seem to be working doesn't look fatal, probably a configuration setting missing somewhere but apart from that everything is good.
Now let's see how much the API's and web services have changed. This beta is certainly significantly faster than Beta 2.
Update: This is the work-around for the issue I was having. Reporting problem with installing Beta 3 on a domain controller.
I don't know how far you've gotten, but you can find an example of using the TFS source control client API at http://blogs.msdn.com/buckh/archive/2005/09/09/463287.aspx.
Buck