after not starting an '89 accord for four months (not a year, like i figured), i jumped it (its battery is known to be shot). while still hooked to the source car, the '89 accord can start and can idle successfully for about 5 seconds, but cannot sustain the RPMs and eventually shuts off. since it was able to run normally for a few seconds, i dont think it's a battery problem, though i will replace the battery. is it perhaps an alternator problem, or is it maybe a carburetor, or something else?

Could be anything. But if you plan on driving this car, do something with the battery. Either charge it outside the car or replace it. Only then can you determine if there are other problems. The alternator only works if the battery has some power in it (to supply the field).