2 master devices on 485/422 cable

My experience with 485/422 is no. I know of no system that allows 2 masters on a network using 485/422

No, you can't do that - but the reason behind it depends upon the communications protocol you are using - and not RS422 or 485 itself. There are quite a few multiple-master multiple-slave RS422/485 protocols around in the industrial world.

To send data from two PC's to a printer you need a print buffer and some fancy handshaking to ensure that each print job is handled by the printer in it's entirety and not interrupted by the other computer. You can buy a "printer sharer" from your local Radio Shack..

HTH, Cameron:-)