Not that this would help music creation very much but I found this at http://www.allps2.net/ps2_cheat.php?game=MTV+Music+Generator+2
View music video:
Enter the options menu, then select "Video Palette". The music video from the Gorillaz's song "Clint Eastwood" can be selected and viewed.
Go to block 999 of the song (the very bottom of the screen) and select the option to enter the author's name. Enter JESTER as a case-sensitive name to unlock a new skin in the skins menu. This is how it looks (altough pic quality is shit):
It looks much better than it looks in this pic. In fact besides the sci fi purple one this one is my favourite looking skin. However, it still won't make me switch from default skin because default skin is the easiest to use and has bigger song screen.
I have to wonder if there were gameshark/action replay codes for the music series. Maybe there could be a MTVMG3 cheat code to use riffs/samples from all 10 artists at once in one single song ^.^. I know apparently new samples unlocks when creating more and more songs in MTVMG3 though. Still doesn't make it better than MTVMG1/2 though