Best of luck. All the start-ups I worked for failed tremendously. DEN was one of the start-ups I worked with. DEN was a joke - a sort of a television network broadcast across T1 lines. It was run by a few ex-Hollywood execs who had no concept of what entertainment was. Terrible stuff.
At least you're getting in on the ground floor. You'll have more ability to control whether the company ascends to being bought out, or decends to the ground.
With three other guys, how could your voice not be heard.
So, did they make you sign a confidentiality agreement?