Thanks DB120 for your answer.
I've checked the manual and the forum and indeed, I have one answer out of two.
No, there is no such thing as midi learn in GURU
(too bad, you should check Ableton Live, their midi learn is awesome!!)
But still, I can't launch nor select patterns from a midi keyboard.
I can launch all the pads, the undo and commit buttons but no patterns.
(and Yes I've checked my Midi canal is correct)
I know the manual says the oppsosite, but it doesn't work.
My configuration : iMac Intell, OSX Leopard 10.5.7, GURU 1.6.12 (official), DIGI 002R, PT8 LE (official)