I solved my own problem, sort of. I reinserted my Snow Leopard installation disk and then went to the Optional Installs package. One of the Custom Installs available there is Printer Support. I loaded "All Available Printers," after which Mac OS recognized my HP 6310. So, apparently, there are drivers in the optional installations package that don't get loaded automatically with the basic Snow Leopard install. Perhaps the missing drivers can also be obtained through Software Update. I did that too, but can't tell if it affected my connection since the scanner worked both before and after I updated the HP software.
In OS 10.5, I typically scanned using Acrobat. Even though my scanner is now working, Acrobat can't find it. This is odd because if I scan through the Print & Fax screen in System Preferences, I can scan to Acrobat. After the scan, Acrobat opens and shows the scanned image in neat old .pdf format. But it won't scan directly, and the System Preferences route takes a lot of extra key strokes. I long for the old HP Director.
