Problem installing HP B8550 printer

I'm trying to add an HP Photosmart B8550 on an iMac running 10.8. This printer is installed and works fine on my Mac Pro Tower running 10.8. The printer is connected to Time Machine. When I add the printer on the iMac, it says Apple has software drivers available - then returns:

Tried everything I can think of. Software Update says no updates available. HP web site says get drivers from Apple Software Update. Original drivers that came with the printer won't install on OS X 10.8.

Any ideas?