Installation Hanging Very Early On

[WFPeifer]

I extracted the 2.5 files locally and then uploaded them to a new directory on an existing (developed in FrontPage, years ago) site with the intention of installing into that directory, getting the site ready and then copying into the root. I'd done it before (with 1.5) so I didn't envision any problems. But almost as soon as I start the install the process goes stupid. At "Step 1" (Language) I picked English and clicked on the "Next" button. Instead of getting to "Step 2" (Pre-Installation Check) I get nothing except the "I'm thinking" circle in the middle of the large white panel.

Any clues as to what's happening here? I watched the circle going round and round for about 20 minutes and went off to take care of a client. When I returned 3 hours later it was still "thinking".