Car died tonight.taking bets(long post)

[todd95GT]

Just ought this 95 GT last week. It's a mint example of a SN95. It's got a cat back, pulleys, and throttle body. When I bought it, it stalled very quietly as I pulled into my driveway. I thought I let the clutch out too much without enough gas, but also thought that it was an awfully quiet way to shut down. Tonight, I was driving and noticed the dash lights were very dim. The battery gauge dipped to the extreme low side of normal. I killed the accessories I had running and dropped from 4th to third to get the alternator spinning. The gauge slowly went back up to the center of normal. As I continued my trip, the needle slid back down to the very low side again. When I neared my street, the lights began to get very dim. As I turned onto my block, I hit the brake pedal to stop for passing traffic and the tach needle dropped to zero even though the car was still running. When I relesaed the pedal, the tach jumped back top normal. It did that two more times-both when I hit the brakes. As I was driving down my street, the lights just died. When I parked it, the car finally gave up and stalled. It wouldn't start after that. It was making the usual ticking sound a car makes when the battery is dead and you try to start it. Now, with the underdrive pulleys, I know the gauge sometimes dips a little low. I've had pulleys in other cars that I've owned. I hope that the battery has just had it---I don't know how old it is and there is no dated store tag on it. Sound to you guys like it's just the battry dying or do you think it might be the alternator. I was thinking it is probably just the battery since when I dropped it down a gear and revved it up, the gauge began to climb further into the normal area. I figured the alternator was doing it's job.
While I have your attention, can anyone answer a window motor question???

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Todd
1995GT Cobra look-alike
pulleys; Flowmaster cat-back; 65mm TB; Cobra R's, front, and wing