yo, I never figured out how to speed up and slow down samples in there, like the Dr. Rex would allow you to change the pitch and shit but not like actually change the tempo (although I was using an old version so it might be easier now),
You can do it two ways. With Recycle (a separate program developed by Propellerhead) you can edit .wav samples and change their pitch, tempo, EQ, normalize, etc etc. That's usually what I do before I load my samples up in Dr Rex. Or you could use the NNXT and do it the more complicated way.
I'll find you some good tutorials and edit later. But in the meantime, torrent Recycle lol.