On a fresh WPMU install, if I choose subdirectories, everything works perfectly.
But, because I'd like to domain map some blogs later, when I install with subdomains, I get a Page Load Error when trying to visit a subdomain.
This is not a WPMU problem, (probably httpd.conf), but thought this info would help others with the same problem.
My experiments have all failed. We have a dedicated server, so I can do anything to it.
Thanks so much for any hints, leads, tips, or links.