Well, whether you're using a piece of software or a real drumkit you're still going to run into the same limitation: yourself.
If you can read drum notation you should probably go check out a couple of books at the library. I know there are a TON of books that talk about different rhythms and have them notated. You could also download a bunch of MIDI drum beats and dump them into a host (free:
ardour | the new digital audio workstation).
I don't really know any good PC-based drum machine emulators. In my experience most of the time "free" precludes "good" when you are talking about music software.
Start with a google search for "drum machine emulator" or "pc based drum machine" and check out these two sources:
Pattern Sequencers - The Sonic Spot
KVR: Audio Plug-in Database (Search Page) - VST, Audio Units, DirectX, LADSPA, DSSI