Ok. figured out how to do it:
<Button Location="157,0" Name="LookupTarget" OnPress="URL='
http://www.lootdb.com/eq2/mob/' ## Parent.Name.localtext
browser URL" Opacity="0.500" PackLocation="right,top" PackSize="fixed,fixed" ScrollExtent="13,13" Size="13,13" Style="/ButtonStyles.tabscroll_left" Tooltip="Lookup target" Visible="false" />