OK Look.
Oeric's MookChat with Hide-a-scroll
Chat input is toggled by turning on and off the titlebar, which is never visible anyway. The scrolls only show if you mouseover the specific area (located on the right). If you use this, the chatpage wont jump around on you. The scrollbar will still cover MAYBE two letters of text on the right, but again, thats only when you hover over the scrollbar area specifically.
Zonx, If it help's I could upload a version of this as an addon to your main download. (Don't know why I should, because it's got its own download.)