Update: I tried the install on a workstation running Windows 7, and it works ok there. This helps me figure out a few things. First, the hang is before the administrator does anything, including creating the c:\arcgisserver directories. Second, the domain user is ok and has sufficient priveleges. Third, it's not a browser problem because I can access the manager page both from the local workstation and the server, using all of the browsers I attempted to use earlier.
Interesting, but not helpful. Still no server.
Any other suggestions?