So you could get a PoE switch, which places the voltage on the wire pairs directly from the switchport, or you can get an injector that is a little box that is inline with the switchport/camera. The injector will have an adapter powering it, and it then sends the power over the ethernet cable to the camera. Usually you'd get a specific injector that is made for the camera, but as long as you know the specs I'm sure there are plenty of generic ones out there.
For a PoE switch, I've only dealt with them in business-grade switches. But without looking, I'd guess there are plenty of consumer/SOHO devices available now on the cheap.