This is what finally worked:
def dowelHelp
dowel_help_File = File.join(File.dirname(__FILE__),"K2_ToolsSupportFiles","k2ws_DowelHelp.html")
UI.openURL("file;///#{dowel_help_File}")
UI.messagebox("Dowel Help Complete " + dowel_help_File.to_s)
end #def dowelHelp
The html file was:
<!DOCTYPE html>
<html>
<body>
<p>
<img src="K2_ToolsDowelHelp.png" >
</p>
</body>
</html>
Thanks
Keith