You must modify the Print Queue Object in NWADMIN32.
Go to DETAILS for the Print Queue object and select the Users tab. By default, you will see the Context that the Print Queue object resides which basically allows everyone in the Context to Print to this Queue. Highlight the Context and delete it. Do the same thing for anything else that may be listed. Next, click ADD and select the individual User you want to print through this queue.
Good luck!