If you have parallel ports on the back, consider something like this
. It'll put the printers on the network, assuming you have one set up, so that each machine can add each printer locally and use them without needing anything else turned on. It should be noted that the particular model I just pointed you at isn't the best, but it has the added advantage of being cheap!
Edit: They also do USB versions but I'm not honestly sure quite how they work, but seemingly the same kind of 'USB printer <-> network' bridge.