Downloaded Network Security 2009 to 3rd Computer. Vista will not allow it to open. What now?

I bought a license for three computers last year. Downloaded to two of them and they work. My wife just bought a new laptop with Vista Home Basic so I downloaded my third package and it will not open. It appears that Vista sees it as “Unknown Publisher” and considers it unsafe to open. I tried to turn off DEP for it and it said the product would not run without DEP turned on.

I would appreciate any help anyone can give me. Why in the world would Norton download a product that didn’t have a publisher ID with it?

Jack