Help with Ie8 vs Ie7 issue.. relative positioning

Here is the code that controls the #ID in question that I am placing with css.

#dp_div {
position:relative;
z-index:300;
left:536px;
top:-36px;
float:right;
display:block;
height:36px;
width:157px;
background:url(../images/discuss_sa_tab.png);
clear:both;
}

And example page is here
http://www.frontendaudio.com/CAD-M179-Condenser-Microphone-p/1637.htm

The element in question is the DISCUSS BUTTON.

There is elaborate javascript that makes this button appear to begin with, so I realize there are many variables at work here ---

Here is my question that may be answerable though.

everything works as it I want it to in firefox, ie7, and safari, but in ie8 - the disucss button that is positioned using the above CSS is hanging just above where I want it.

I would seem like the registration points in ie8 are different from ie7 ---

I am forced to use this javascript to get that tab to appear there -- so I am specifically looking for a difference in the ie7 and ie8 display of that button using CSS - and hoping for a hack for ie8 of some kind.

Thanks!