Make sure you have Appletalk activated on the iMac's ethernet connection. You may need to download something like Gimp Print to get it to work, I think I had to do this in order to get my LaserWriter Select running with OS X but it was so long ago I can't really remember. IIRC, printer setup and support is generally better in 10.4.
Also, the order in which you power on the Mac, printer and bridge can sometimes also affect it. With my setup powering on the bridge (mine is a Dayna EtherPrint) first, then the Mac, then the printer tends to work best. These old Apple printers take a minute to show up on the Mac after they are switched on so bear this in mind.
Good luck!