Two Computers One Printer

That all depends on which printer you have. If it supports a network connection, you can connect the printer and computers all through a router or hub, available for about $50 or so. It also depends on your current hardware configuration. Are the 2 systems already networked? (ie. sharing an internet connection)

Printer switches are pretty much obselete and you likely won't be able to buy one new. If you can find a used one, there is nothing special to hooking it up. The parallel ports should be clearly marked. And there's no extra software or configuration necessary.

To get a definitive answer, you will have to provide more information about your hardware.