[jpk]

This is called a condensate pump. You can get them at Home Depot in the HVAC section. Don't worry too much about matching specs for a replacement, they all pretty much do the same thing and work the same way. If you have a very long run for the output hose (>50'), or if it needs to lift the water high (>8') get one with a more powerful motor if you can.

Take the cover off the motor (the screw near the ports) and you will be able to see the float switch; it should be a rod extending down into the tank, and a microswitch with some wires attached feeding power to the motor. Carefully (keep your fingers out of the switch) lift the rod untill the switch makes contact and see if the motor runs. If it just hums or makes a screetching sound, the pump will need to be replaced. If the motor runs, but the water desn't move, the output hose is likely plugged (like Hugh said)