you'll probably get best results by midi-sequencing the drums... software like fruity loops is good for "4 on the floor" dance music, but if you want to get intricate with the parts, hand-constructed midi is the way to go. also, you should make sure that the sequencer allows you to change time signatures and tempos freely withing the song.
as for the virtual drum machine itself, i use steinberg's LM4, and it's pretty killer.