After a couple of months where everything worked well, recently my
iMac frequently loses Internet connections (it's connected by ethernet
cable to the AirPort Extreme Base Station). I've gotten this problem
mostly resolved, but still have a printing problem.

When I print to an HP Deskjet connected to the AirPort Base Station,
the print job often doesn't go through, even after printing without
problems moments earlier. The print job stays in the Print Center.
Unplugging the printer's USB cable and then reconnecting it is a
temporary fix -- the printer starts immediately. But the problem soon
returns. Sometimes I have to disconnect and reconnect for every print
job.

The iBook, which has an AirPort antenna, connects and prints without
problems.

Suggestions?

Thanks!