Could you clarify which ibook you have?
I'm assuming you have a G3/G4?
My experience with G3 iBooks is that their keyboards and logicbords need to be replaced on a *rather short* ongoing basis. My friend's G4 also need to have its keyboard replaced twice since he bought it less than a year ago. We had one (G3) with similar arrow problems, and the command key had issues aswell. The keybaord needed to be replaced, but your problem could easily be a bad contact under the right arrow key. If you're not still under AppleCare than your best option is to open the board up (only do this if you feel reasonably comfortable doing so) and check for obvious obstructions. Like discoforce said, a light blast with some compressed air usually gets little bits of anything that can take up residence in your keybaord.
Best of luck!!
PS: If it is a G3, what does it the keyboard smell like? Ours have a pretty funky odor about them...