We've managed to get our Epson 5000 (not supported by Epson under Mac X) working with Gimp-Print after a bit of head scratching.
The Epson 5000 (which replaced our Epson 3000 which committed suicide
by attempting to eat the cardboard so-called 'support sheet') has the Epson ethernet interface card thingy.
The only way we could get it to work (other than via our Appleshare 6 file/print server) was to assign the printer an IP address, then use the IP address option (but, confusingly, not the Epson IP option) in the Print Centre when adding the printers. To give the printer an IP address we had to use the Epson MacAssist software (available off their website in an obscure location) and which only runs in System 9 (or, I guess, in Classic). This 'injects' an IP address into the printer's interface card, albeit that the default IP address that the programs suggests is 192.168.192.168, which doesn't work
...changing this to a more conventional address (in our case 192.169.1.46) seemed to do the job. This now allows the printer to directly receive print jobs from both Mac X (via IP) and System 9 (via the old Appletalk method).
Although, generally, a total pain in the a___, one useful feature of Gimp-Print has been the fact that we can now also use our HP 450C plotter as a printer, as the drivers are included. The complication here is that you still need to give the plotter (which is connected to our ethernet network via a HP Jetdirect box) an IP address, and the software to do this only runs in Windows, so a quick session of Virtual PC was needed...
The only remaining problem....our ArchiCAD 8.0 still won't print to any printer
(but will plot). Luckily, Plotmaker will print fine, and we can save ArchiCAD files as PDF documents and then print them. Heigh-ho.