Still no luck here.
I downloaded another copy of AdbeRdr90_en_US_Std.exe from ftp://ftp.adobe.com/pub/adobe/reader..._en_US_Std.exe And ran it. The Adobe Reader 9-Setup window shows "Processing" as a progress bar, got to 99.98% complete for "Processing" as before, hesitated a few seconds and then turned on my Epson scanner's Copy Utility (!) as before. I let things sit a few minutes, since I know that if I close the Copy Utility window the Adobe Setup window will also close. Nothing further happened. (Antivirus program was disabled for all of this.)
I guess I will just make do with Adobe 8.1.2. (Or eventually switch to Foxit.)