pci_raid, before you go to all the trouble of changing water pumps...
When you start the car, take the radiator cap off, and wait until the thermostat opens. Looking down the neck, do you see coolant flowing, coming out of the rows of the radiator tubes?
If you do, put the cap on, and make sure pressure is building.
Make sure the lower radiator hose is not collapsing. Is there a wound spring inside the hose?
Check the above before pulling the water pump. If any of the above is the condition, it could be the pump, but it's VERY rare for a pump to fail without obvious telltale signs, like pissing fluid out the weep hole.
If fluid is not moving, it could have somehow detached the impellar from the shaft, but it's unlikely. Anyway, check the above first to make sure you're getting some flow, and check that bottom radiator for collapse after it's warmed up.
