To actually answer your question (and welcome to the forums -- love your user name!), there are a great many online tutorials
right here. And, the very basic functions really are easy -- it's literally:
- Set up your MIDI -- the Help file should have that in great detail
- Pick a musical style from the Style Picker (the button that says "Style" just below and to the left of the name of the song) -- if it says it has to rebuild, click Yes
- Input chords (up to four in each bar) -- e.g., C, D7, Am, Bsus, whatever. If you want two chord changes in a half-bar, separate them with commas
- Click "Play"
That really, really is all you need to do. And we promise, we answer questions here, and we don't bite. Much.
As to the other stuff... as silvertones says, getting RealDrums and RealTracks will give you a quantum leap in sound quality. And they work together seamlessly with MIDI. And your computer sounds plenty beefy enough. (I too have Win7/64 and 6 GB RAM -- what processor do you have?)
Interface: What precisely do you want to interface with, i.e., what are you using with BIAB -- a keyboard controller, a hardware synth...? Give us a little more info, if you could.