You have used a huge negative margin to get your categories heading positioned; maybe this is not sitting well with IE7.

stylesheet.css (line 900)
h3.leftBoxHeading, h3.leftBoxHeading a {
color:#FFFFFF;
font-size:1em;
margin-left:-100px;
}

Change to

h3.leftBoxHeading, h3.leftBoxHeading a {
color:#FFFFFF;
font-size:1em;
padding-left:23px;
text-align:left;
}