You can use just the FSDT installer even with a boxed version, and there's no need to install the CD installer, run only the downloaded one.
If your boxed version was already active on your Windows installation, you don't have to do anything, it will run as fully registered. If, instead, you are reinstalling Windows or lose your activation for any reason, you can reactivate it, by selecting "Register Serial" from the Addon Manager menu for KLAX, and insert your Serial Number, as reported on the CD case.
Basically, you can forget your CD, the only thing valuable in your box, is the Serial Number...
