Lexmark Z55 won't work with a print server

First, sorry is this subject has been brought up before, but I didn't have the time to check it out in here, and it's a pressing matter for me. If it has, please give me the link or directions of some kind.

The enviroment: small office network, 5 pc's with win98, 1 broadband US Robotics broadband router, broadband internet conection (via cable modem), 2 printers - a Z11 Lexmark and a Z55 Lexmark (new).
The router has 4 switch ports, 1 wan port, 1 serial for a back-up connection and 1 parallel port for the print server (included in it).
The Z55 can be connected either via usb or parallel cable. Z11 can be conected only via parallel cable. They both work ok connected directly to the pc, via the parallel cable.

The problem: The Z55 doesn't work conected to the print server (the router comes with a driver for a printer port that is instaled on the pc and must be selected in the printer settings instead of lpt1). The printer must be instaled as a local printer. The ip of the printer port is set as needed. I tried 2 types of drivers for the Z55 but neither work.
The Z11 works ok on the print server, having no problem.

A solution: A friend of mine sugested that I use the driver of the Z11 for the Z55 but the printers are quite diferent. Didn't try it yet (tomorrow I'll go to the client) but I'm not convinced that this will work.

If you have any sugestions, I'm looking forward to hearing them. Thanks alot.

Romania is a beautiful country, unfortunately it's inhabited.