I had the same situation, with pratically identical hardware, back in March. While you could spend a little time trying to think of an elaborate way of doing this with switches, it's not worth it. For $129.00 go out and get the Epson 740i. It has a parallel for the HP, serial for your 800, and USB port for the G4. Not to mention, you'll gain a little more speed using the 740i.