Thanks. That got me to the partition and reboot step. I made the Bootcamp support flash drive and a Windows 7 USB drive from the Microsoft utility and inserted both. When the Mac rebooted, I received the no bootable device error and am stuck there. I guess I'll poke around some more to try to figure this out
This seems more difficult than when I last installed BootCamp under Snow Leopard (old, I know).
OK, got it all installed. I misread the instructions for Windows Support Software, thinking that USB was to be plugged in before Win install - not so. Also, Windows 7 USB/DVD Download Tool did not make a bootable USB that the Mac recognized. So the solution path for me, working with a windows ISO image was:
1. Use Daemon Tools to mount the Windows iso image file to allow Bootcamp to start
2. Use Bootcamp to make the bootable USB drive from the iso file.
3. Set up Bootcamp partition with Bootcamp Assistant.
4. Reboot to install Win7. Couldn't install on the Bootcamp partition, needed to reformat to NTFS.
5. Wireless Mouse/trackpad did not work during Win7 installation. I had to use keyboard only.
6. When Win7 installation was complete, tried to run Windows Support Software, which was needed for 64-bit versions of windows, according to DL1638. Did not run and reported not compatible with this Mac(!).
7. Windows 7 Ultimate now installed and up and running.
A curious observation on the Windows "experience index". This iMac has a PCIe connected SSD yet the disk performance reported by Windows came in at 5.9. All other indices were 7.8 - 7.9. (7.9 is the highest value.) I don't know whether this is a Win7 issue or what.
In any case, all appears to be up and running successfully. Thanks for your help and persistence.