IE6 vs IE8, button vs hyperlink, CSS rendering issue

Given the following sample form code and CSS stylesheet

Form

<div class="Center_300 ">
 <button id="KeaneDelegate" runat="server" class="button_red2" causesvalidation="false"><span>Keane's delegate view</span></button> 
<br />
<br />
<a class="button_red2"> <span>Keane's delegate view</span></a> 
</div>

css

.button_red2 
{
background:url('../../images/button_red_left.gif') no-repeat left top; 
display:inline;  
float:left; 
font-size:12px;  
font-weight:bold; 
line-height:16px; 
height:21px; 
padding-left:9px; 
text-decoration:none;
border-style:none; 
color:White;
 }
.button_red2  span
{   background:transparent url('../../images/button_red.gif') no-repeat top right; 
padding:3px 10px 2px 0px;
border-style:none;
display:block;
}

.Center_300 { width:300px; margin:0 auto } 

When viewing this in IE8's compatibility mode (IE6), the button is rendering correctly but i get 'blank' spaces to the left and right of my text. the hyperlink renders correctly

When i switch back to native IE8 mode, the button renders correctly, as lenghty as the a hyperlink but there's a slight misalignment in the sliding door, the right part seems to be shunted 1 pixel down

If i then remove the block alignment and adjust the padding , it renders perfectly (but no longer the hyperlink)

.button_red2  span
{   background:transparent url('../../images/button_red.gif') no-repeat top right; 
    padding:3px 10px 3px 0px;
    border-style:none;
 }

But switching that back to IE6 mode makes it even more uglier

I'm trying to use a button, not a hyperlink for my forms but from the CSS style I got delivered, only the hyperlink renders perfectly between various IE versions.

Why is there that extra space in the IE6 rendering on the button? Why does it appear a pixel out of line when back to IE8 mode and how can that be sorted? Or is it not solvable?

Below the 2 gifs for the sliding doors.

I think it is caused by the button bug in IE which is rendered too wide. Have a look at this article: http://latrine.dgx.cz/the-stretched-buttons-problem-in-ie