The best way I can describe where it is:
Stand in front of the engine. To your left, follow the wiring that goes down the front left of the engine and plugs into the crank and cam position sensors, as well as the front oxygen sensor. The oil pressure sender is plugged into a single wire which comes out of that harness--if you follow the wire, you should find the sender on the other end of it.
You can't see it except from underneath..I'm pretty sure that the sensor is vertical.