HP Laserjet 4mp won't print with Snow Leopard

My great Laserjet 4mp prints just fine with OS 10.5.8 but not with Snow Leopard (10.6.2) on my new iMac. Have spent three plus hours with senior level Mac Techs to no avail. The printer screen shows the correct printer and driver and indicating valid connection, but when attempting to print I get the message "Unable to print, try again in 30 secs". Since 10.6 doesn't have Appletalk, am unable to use it; techs have tried to use the 4mp driver supplied with Snow Leopard and also downloaded it separately from the web site. We (they) have also tried using all methods (IP, Daemon, and HP Jet Direct using Ethernet and Serial to USB connections). Techs have talked with HP techs and have no other solutions. The security system is off. Any suggestions are welcome! Thanks!