What you need for a decent drum track are:
- A good set of samples. freesounds.org, I think, has a few useable ones (notably the ones by 'ltibbits' and 'tic tac shut up' are quite decent, though heavy on the ambience). Good kits have multiple samples per instrument for different velocity layers (especially with cymbals, this becomes very audible, because a cymbal has a 'crash' point, above which the spectrum becomes a lot richer and less bell-like), but also for various playing techniques (rim shot, rim click, flam, roll, etc.).
- A sampler. Most DAW applications have a built-in sampler (e.g. Logic's EXS24), otherwise, I can recommend Battery (not free, but an excellent drum sampler).
- Some drum programming experience so that the tracks you program sound natural; actual drumming experience helps judging what is playable and what isn't. And of course time. Which is why I'm not doing it.

Groove Agent is an amazing piece of software, is really useful to create real "natural" drums tracks.