The element that's showing is
div#twtr-widget-1 .twtr-widget .twtr-widget-profile which is styled in your CSS with this -
The element that is hiding behind #bg is an unstyled anchor.
font-family: "lucida grande",lucida,tahoma,helvetica,arial,sans-serif !important;
font-size: 12px !important;
Either give that anchor styling that's similar to .twtr-widget (it will need position: relative
Adjust #bg's position in the stacking order with this bit highlighted in red -
background: url("images/header-bg.png") repeat-x scroll 0 0 transparent;