iPhone - Create a semi transparent rectangle with opaque text

I have a MapView and I want to display a black semi transparent rectangle on top with a text inside. Not over the entire map only on section of it (maybe on the top corner) just as an info box (like the one in the iPod player that appears on double tap and displays the Mute and skip buttons).

I tried google but I'm not getting any clear answers. How is the best way to accomplish this?

Thanks in advance

Can be easily done with interface builder:

View Hierarchy

NOTE The background has to be a separate view which is the first entry in the list of controls, so it is in the background. Setting the container view to an alpha value below 1 will also be inherited by the subviews, which is not displayed in the interface builder