ObjectDesktop is a suite of apps. Not just one. If your apps aren't in your Downloads page at Stardock, then try downloading ObjectDesktopManager, use your serial/login there to get your apps.
Well, if you have the serial, just install the product, it will ask for serial. Put it in and you're good.
If by chance it doesn't ask for the serial, open the product, go to "about", choose activate. Put in serial.