Jamie, we did take apart a new water pump to have mine powdercoated. Here is a pic of the removed bearing and impeller assembly. The hub is also shown.
You'll first need to press off the hub that the pulley bolts to. Then with a deep well socket or other press tool, you can push the whole assembly out the back of the pump without removing the impeller. Like Randy said, be sure you press on the outside of the assembly, not on the shaft itself.
Be sure to have the aluminum housing of the pump supported around the impeller as best as you can. A 3-4" diameter piece of pipe would be best. Something that is just bigger than the impeller diameter. We broke an old water pump housing as we were figuring out how to do this!
For reassembly, you can heat up the aluminum housing and even put the bearing assembly in the freezer over night so the press fit is not so tight. Use a little anti-seize on the outside of the bearing assmebly and then just press it back in by pressing where the shaft is in the impeller. The press fit will not be tight enough that way where it would damage the bearings. Mine has gone 3 years and 17,000 miles.
It should press back into where kinda green looking ring on the seal is flush against the housing. Then you can support the shaft at the impeller and press the hub back on up to the notched area of the shaft.
Just watch as it comes apart and you should have no trrouble with the reassembly process.