Am I able to make the change I'm looking for? I have tried googling for this but with no real success. Would be very grateful for advice and comments.
EDIT: Just had a thought. What if I leave iTunes itself on C but copy the music and video files to D. Then delete the music and video from C. iTunes will then not be able to find them but I could go to "Add file/folder to libary" in iTunes, point to the new locations on D and re-import them from there. Would that work/be OK? I'm just a bit scared I'm going to screw things up and be left with an iTunes library mess.