This is the code I have used.
<script type="text/javascript">var timer_id;function scroll_iframe(frm,inc,dir) { if (timer_id) clearTimeout(timer_id); if (window.frames[frm]) { if (dir == "v") window.frames[frm].scrollBy(0, inc); else window.frames[frm].scrollBy(inc, 0); timer_id = setTimeout("scroll_iframe('" + frm + "'," + inc + ",'" + dir + "')", 20); }}function stopScroll() { if (timer_id) clearTimeout(timer_id); }</script><style type="text/css">html { overflow-x: hidden; overflow-y: hidden;}a {text-decoration:none}a:link {color: #666666}a:visited {color: #666666}a:hover {color: #000066}a:active {color: #000066}</style><table border="0"><tr><td height="70" align="center" valign="top"><img src="header.png"/></td></tr><tr><td align="center"><table align="center" border="0"><tr><td><img src="scroll.png"/></td><td><div class="arrows"> <a href="java script:;" onmouseover="scroll_iframe('disp', -4, 'v'); window.status='Hover here to scroll up.'; return true" onmouseout="stopScroll(); window.status=''; return true"><img src="up.png" alt="" border="0"></a> <a href="java script:;" onmouseover="scroll_iframe('disp', 4, 'v'); window.status='Hover here to scroll down.'; return true" onmouseout="stopScroll(); window.status=''; return true"><img src="down.png" alt="" border="0"></a></div></td></tr></table></td></tr><tr><td align="center"><IFRAME SRC="port.html" frameborder="0" height="350" width="600" id="disp" NAME="display"></IFRAME></td></tr></table>