With NT 4.0, you can modify these entries on the "Print Server" by using
Start / Settings / Printers / File / Server Properties / Advanced.

To do this via the Registry:

To prevent PopUp messages from appearing upon print job completion:
To prevent PopUp notification: add a value name of NetPopup, set REG_DWORD to 0. To prevent logging: Add VALUE: EventLog set Reg_DWORD to 0.

You will have to stop and restart the spooler from services in the Control Panel but you may wish to reboot.