I'm using Music Creator 6 and M-Audio KeyStudio49 without problems. But I'd like to perform using two instruments at the same time (one with each hand, what's usual in keyboards like yamaha psr line for example) spliting the keyboard in two ranges. Is this possible with Music Creator 6 ?

Welcome to the forum.
That's usually a function of the keyboard. Check it's manual to see if the keyboard can be split, transmitting MIDI data on two different channels.
Then set two tracks in MC to receive on the two different channels.

sounds plausible. I played in a band where the keyboard player had a Yamaha piano that could do they split keyboard thing.... I don't know if it uses 2 different midi channels to do that or not. But Greg is correct... if it does, assign one to one track and channel and the other half to a different track and channel..... set up the tracks with synths and samples and set the channels and you're off to the races...

Ok. This seems to be the better solution. Unfortunately I didn't find this option in the KeyStudio49. Thank you.

your best bet is to record two midi tracks then just delete the unused parts you dont want..if this is for live purposes..well scratch that..but in piano roll this can be done rather easy after recording.
just drag down the notes of your left hand and delete them for your right hand channel/vice versa the left hand