Well, you may have two problems (bad alternator and bad oil pressure) instead of one, but your more immediate problem is that your alternator isn't charging the battery, so deal with that first. Get yourself a replacement alternator (something with a decent warranty, as Bonnes like to eat their alternators anyway) and install it yourself -- it'* not difficult -- and then with the engine running on a more generous supply of juice, see what your oil-pressure readings are.

If the oil-pressure gauge is still going dangerously low at idle, inspect the sending unit to see if it'* leaking (shouldn't be wet with oil on the outside; replace it if it is) and try temporarily installing a mechanical gauge, to see if its reading agree with what the factory gauge was telling you. Let us know what you're seeing when you get that far.

on other thing that wasnt mentioned check all battery connections for corrosion that could be a problem as well

If your not real mechanically inclined, do yourself a favor and draw yourself a "roadmap" of the belt routing before you remove it. Some cars have a sticker under the hood showing this but some do not (sticker missing). Might save you a half an hour or more of trial and error when it comes time to putting the belt back on.

Oh, Duh... you're absolutely right; I forgot about that. One thing you might want to especially check is the contact ring inside each of the battery terminals. You need to press the center bolt back out of each terminal. (With a wrench, and your thumb pushing up on the end of the bolt as you unscrew it, you can work it out.) That will reveal a metal contact ring molded into the rubber end of the cable, and it probably could use some wire brushing and a little dielectric grease or Vaseline. Clean up the bolt itself while you have it out, too.

You can see the underside of that ring by just looking at the underside of the cable connector, but its top side makes contact with the bolt, as well as being pressed against the threaded socket of the battery, so cleaning the top contact surface can help a lot.

-- Andy

On that same note, I've had the positive battery cable corrode internally on both my 97 SE, and my wife'* 2001 Grand Prix GT (both with the same 3800 engine). In both cases there was no real external evidence that the cable was corroded inside it'* protective cover. The symptom was just like yours, the voltage meter would dip when you turn on the lights, run the AC, step on the brake, etc., but the real kicker was when you'd drive someplace and shut off the engine, then try to start it a few minutes later and it wouldn't start. It'* easy to diagnose after replacing the battery and the alternater and still having the same problem.

In theory you should be able to test the resistance of the cable with a digital ohmmeter, looking for any significant resistance. Being a giant conductor, the cable should normally have near zero resistance.