Muggi, another thing you can try doing is (and I'm not sure of the proper name for it) but "half-one arm chinups"). Basically hold the bar with your right hand, and with your left hand, instead of holding the bar, hold onto the wrist of your right hand. That way your right arm has to do much more work, but your left can still help to the point that you can pull yourself up. And of course reverse for the left...