How do I show the description box of the properties window in Visual Studio 2010 if it is hidden?

I had the same problem and it was caused by the description box lenght having been dragged to zero. To solve the problem I had to un-dock the properties box and resize it as long as possible. It is then just possible to find the verticle resize cursor at the bottom and resize the box.

Right click and select "Description" menu item.

If the suggestion by Alex doesn't work, an alternative is to click WINDOW > Reset Window Layout.

Warning: This will reset every window so best used only as a last resort.