It's at the front of the engine - drain coolant, remove the serpentine belt, remove 5 or 6 bolts holding the pump, install the new one. You may also need to pull the radiator shroud to get access to the front of the engine.
If this is one of the last 5.7's, the pump is located just above the distributor (what moron would invent that setup?!?), and usually when the pump develops a leak, the distributor - a solid state obscenely expensive thing - goes out immediately.
