How to keep a printer invisible to other part of network

Question

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. This isn't the first time this has happened.

Answer 1

At its simplest, you'll partition your network.  That can be via a managed switch with vLAN support, or by connecting up an IP router which will inherently block the typical Bonjour traffic — which is likely how the printer is being detected here — or via a firewall connected at the cable modem and particularly that has support for multiple network segments and run those to the different areas (which will keep the networks quite separate). 
Of these, the latter probably most closely meets your needs; the firewall.  Particularly because that can be configured to block other traffic between the LANs; more than just the Bonjour chatter will be blocked.  Locally, I'm using various ZyXEL ZYWALL USG series firewalls, which does have support for multiple local networks (two LANs plus a DMZ are common on various of the low- to mid-range models).  (I've not tried the USG without NAT, but the device does have options to do that.)
You don't want to have two devices both doing NAT here, so either disable NAT at the cable modem and use a firewall that does NAT, or — if you can't switch the cable modem into its bridge mode, or the modem doesn't support bridging — then you'll have to avoid allowing any NAT at your firewall.