keeping a printer invisible to other part of network

I share a cable modem line with a suite mate (professional office). my equipment is plugged into my switch, and the switch is also receiving a feed from the cable modem. When my suite-mate had someone print some work, that work went to my printer instead of the suite-mate's printer. How do I make sure that my printer never appears as an available option? I am using Mac OS 10.7.5 and the suite-mate is using Windows XP through WIndows 8. In fact, this situation is a cause for concern, because we both need to assure that no other parties can wander into and through our files.