For me, the app that had stolen port 80 was Skype. I must have been asleep or temporarily insane when I turned that option on in Advanced/Connection: "[x] Use port 80 and 443 as alternativse for incoming connections"

But, the Windows 7 Resource Monitor is a thing of beauty. I just click on the Network tab, opened up Listening Ports, and there it was. Wish I'd remembered that utility before uninstalling/reinstalling Apache twice, yanking all the customizations out of httpd.conf, and turning off and on about half a dozen services

Oh, and I do have Acrobat 8.1 installed and running, from CS3. I think maybe the CS3 is using a different licensing service.