Thanks for the quick help, Justin.

It turns out that this can be fixed by enabling "Compatibility View" in IE8 (Page/Compatibility View). I guess MS put this setting in IE8 because it knew that some pages wouldn't render properly. Enabling this setting puts voipo.com in the list of sites that need it. Ironically, I used this setting only one other time (which is why I forgot about it), and that was with msn.com.