Electrical problem. :(

[B 4 You]

I was driving around today (unsuccessfully) job searching when i noticed my battery, stop lamp, and parking brake lights all came on at the same time. They were really dim though, as I stepped on the throttle (increasing battery voltage) they dimmed further and shut off. Then as soon as it went to idle, they were back on. It idled fine, the headlights weren't dimming of flashing, and I drove back to campus without any problems. The ABS light also started coming on, also dimming/brightening with voltage change. My first inclination is the alternator. Could it be worse than that? I thought all the lights in the Christmas tree would come on if the alternator was going.

If it is the alternator, how big of a deal is that to change? Could I do it myself? Would you do it yourself?