Electrical problem or what

Recently the battery in my SC2 wouldn't hold a charge, the culpruit, the alternator. After following the excellent instructions listed here on how to replace it I thought all was good to go. That was until recently, when I started it up and the ABS light came on, then after a minute or two, once the engine was warm, the Service Engine Soon light came on. All too similar to when the alternator died, but this time the battery seems to be holding a charge which I am guessing that means that the alternator is working. So ignoring the warning lights, I took it down the road (less than 1/4 mile) and the engine died just like when the battery died, but it restarted. So I turned around and the engine died again, got it started and went a little further and it died again. Weird, all the lights, radio, etc, worked and the car started back up.
The car has now sat in the driveway for 2 weeks. I went out and it started right up, but once again the ABS light came on and the Service Engine light came on once it had warmed up. I drove it again and it seemed fine except for the warning lights. But, something I had not noticed before is that the power windows do not work now and the Traction and rear defrost "lights" don't come on when depressed.

Anyone have any clue what might be wrong??

if you have a multimeter, test the system voltage, should be 14+volts. did you have the alternator tested before replacing? cables tight? belt slipping? oil leak above alternator? if you think the alternator is really bad, have it tested, find out whats killing it, and hope its under warrently