Wireless Printer Sharing Problem

I have three Macs, two have their own printer. The first mac is a MacBook Pro connected wirelessly to my network running 10.5.1 and connected to an HP printer via usb. Th second is a G4 running 10.2.8 hardwired to the same network connected to a different HP printer via usb. The third is an IBook running 10.4.11 connected to the same network wirelessly without a connected printer.

I can get the IBook to print on either printer simply by enabling printer sharing on the MacBook Pro and the G4. The G4 will also print on the MacBook Pro's printer. The problem is that the MacBook Pro will not print on the G4's printer. It doesn't even show up as a possibility.

I don't understand why the IBook can print using the G4's printer but the MacBook Pro can't. Does anyone know the answer to this?

Thanks in advance