Gunner B

I recently (today) bought windows 7(upgrade) to install on my macbook using bootcamp, and it succesfully worked as i am using it right now. the only problem is when i went to "activate" it using the product key an error came up saying "...only be used for upgrading, not clean installations". how frustrating that i spent around 100 dollars and cant activate it. can someone please help me get this activated, or do i even need it activated? is there some type of keygen? PLEASE HELP.