Depends what Im using...sometimes Ill do the bass on the MPC, sometimes itll get done in FruityLoops w/ the midi controller, or sometimes my bro lays down the bassline w/ an acoustic bass.
Uh, I guess I open up Fruity Loops. I find subwoofer and mess around with tha differnent notes, until I hear something I like. Then I just put it down on a Piano Roll.