I can tell you why it's not working. It's because the display of the sub-list only occurs when the cursor hovers over the anchor element in the tab (i.e., Pricing and Galleries). I seen this feature on a bunch of web-sites so I know it can be done. If you know of one, you might try using Firebug on Firefox to see how it was done.
Here's a site using pop-ups although it's table based.
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After our discussions, I think I have the fix. In following css element, I changed the height from 25px to 30px.
#primary_navigation ul#menu li#active a.r span.l span {
background:url("../images/tab_body.png") repeat-x scroll 0 0 transparent;
height:30px;
padding-top:5px;
}
I tried 26-29 and they didn't work. The larger height is extending the hover area 5 pixels downwards so it's in contact with the sub-menu. When it didn't, you left the hover area before entering the sub-menu.