the pros usualy start with a drum track.
I usualy (turn on the metronome), record a track with chords maybe melody that the whole song will rely on, then add drums, bass etc..., than erase this first track that you created.
It really takes a long time to actualy be good at this, and you gotta think ahead when you're recording. All this can be done with just a keyboard that has a sequencer in it. it takes lots of practice and stuff

check this forum: http://board.midibuddy.net/

Is there software that can isolate the various instrument parts from a CD, say with maybe a very good equalizer? I know there is software that will create a midi file from a CD, but most folks say it doesn't work well.
Starkeeper