Printer problem: PC/MAC

I am a fairly recent switcher from PC to MAC (iMac G5). When I set up the Mac, I moved the printer (HP 7960) to the Mac's USB connection, because most of my printing is from that machine. Both computers are set up on a wireless LAN. I can see the Mac over the network from the PC, but I cannot print from the PC. File and printer sharing is set on the MAC to share.

Any ideas? Thanks, Pete