The whisky inside is probably Beam Choice which was usually 5-8 years old, of course whisky doesn't improve with age once it's bottled. Not a rare whisky, (rather common actually) but the decanter (this is the square box, right?) does have some collector appeal. I would drink the whisky and sell the container.
Can't help you as to value, perhaps this link would be useful:
http://www.jimbeamdecanters.net/jim-beam-guides/