Yamaha DTXpress/DTXplorer/DTXtreme

hi,

i am doing GCSE music (dont know the american equivelant, its 
important though, im 15, do the exam when i'm 16).  anyway, i took 
this after being told that I could do basically all the work on 
drums, it was a very open ocurse etc.  8 weeks into it, it has been 
all melody work.  Now, I have to compose a melodic piece, and I have 
2 weeks.  I only play drums, and I was talking to this guy that works 
with 6 of us musicians that don't play classical like the rest of the 
class, and we think that i can put chords and a bassline on my kit.  
Am I right? can i put a bassline on my bass drum that changes every 
time I hit it? can i put a chord on, say, my snare? how do I do this? 
can I change the voices? Can I record guitar voices from the computer 
onto my kit? where could I get these? Can I change the length of each 
note etc? Does MIDI help? If so, explain it like your talking to a 
dummy because I dont have a clue about MIDI.  Sorry for all the 
questions but its a vital piece of work.  PLEASE HELP!

Joel