Transparent PNG in AdRotator - Applying Behavior

I'm having a bit of trouble with AdRotator. I have images that are transparent PNG files. I created a style that applys the behavior to correct IE6 inability to display transparent PNG images. When I add the reference, images don't appear. They work in FireFox, just not IE6 (I haven't checked IE7). This behavior works everywhere else in the site.

Is there a workaround?

<asp:AdRotator id="AdRotator1" runat="server" borderstyle="None" datasourceid="SqlDataSource2" cssclass="adRotator"></asp:AdRotator>

.adRotator {
behavior: url('/behaviors/pngbehavior.htc');
border: 0px;
padding: 0px;
margin: 0px;
}

You need to haveheight andwidth set in AdRotator or CSS.