How do I set selected Menu item in a asp:menu control?

[goran.strand]

In my Default.aspx I have a Menu control
(System.Web.UI.WebControls.Menu) with some static menu items. When I
click on a menu item, the navigate URL contains another aspx page that
I load in an IFRAME, like this:

<asp:MenuItem Text="GALLERY" Value="Gallery"
NavigateUrl="~/gallery/Gallery.aspx" Target="mainFrame"></asp:MenuItem>

The problem with this is that the Menu Item GALLERY will not show as
selected since there is no postback to the page Default.aspx, is there
a way to solve this? I want to load my content in an IFRAME since I
don't like when the header (containing my menu) reloads and dissapear
for a short while before it's reloaded.

Any sugestions?