DIV hover bug in IE 8, cant figure it out

Any help is good help. This is the page in progress, hover on the Try It Now button in the middle of the page. It grows in height and pushes the rest of the content down a bit when viewed in IE 8.
http://www.creditscorequick.com/theft/index2.html

Here is the button code
<div align="center" id="button1"><a href="https://www.trustedid.com/cmalp9.php?promoRefCode=NEXTWEBID30" target="_blank">Try It Now!</a></div>

Here is the css:
#button1 {
font-family: "Trebuchet MS", Helvetica, sans-serif;
font-size: 18px;
color: #000000;
background-color: #E4E4E4;
height: 30px;
width: 120px;
border: 1px solid #C0C0C0;
font-weight: bold;
text-align: center;
vertical-align: middle;
margin-left: 70px;
margin-top: 15px;
-moz-border-radius: 8px;
-webkit-border-radius: 8px;
line-height: 29px;
display:block;
}

#button1 a {
color: #0058B0;
text-decoration: none;
display:block;
}

#button1 :hover{
color: #FFFFFF;
background-color: #00A400;
border: 1px solid #009F00;
text-decoration: none;
cursor:pointer;
display:block;
-moz-border-radius: 8px;
-webkit-border-radius: 8px;

}

Regards,
JB