You're not the only one who has had trouble with this. I've heard that some people jump on the wooden fence and then jump up into the honeycomb with the cash. But most people jump into the left (it might be right. Ack, it's been a while, but trust me you can't miss it.) honeycomb hole and go inside. That takes them higher up. Then you'll see another honeycomb hole a bit higher up, you jump to that top honeycomb hole go inside and the cash will be there. I hope I explained that well.
Oh, and to do the high jump, you make Conker duck (left trigger button I think...) and then you just hit the jump button.