I will explain this only ONCE:
Load a sample. Go to param screen (function f6) where you can change the pitch and decay.
Make sure you that is sample you want and the sample is set on mono and not poly.
Highlight decay and hit OPEN WINDOW.
(this is going from memory since I dont have my MP in front of me)
you can see some values 0 & 100 at the bottom of the list.
Switch them (make the zero value 100 and the 100 value 0).
Now, go back to main screen and hit 16 levels.
make sure the sample you just edited is the one you want. Leave the default settings as velocity.
BAM! You are done!
hit all of your pads.
chop chop chop chop chop ..
if you dont like where it is chop, go to your edit screen and edit the wave.
I hope this helps...I am at work right now so I am not looking at it.
--DJ Ambush