When we first got our store going, my lawyer encouraged us to have a checkbox that customers must click that signifies their agreement to our licensing. My problem was that I didn't have the programming skills to make it work. So, I contacted by friend Jay who made it work for me. Since then, I've been contacted by other e-junkie customers looking for a way to implement the checkbox in a similar fashion.
Being the kind soul that he is, Jay has shared the code that works to create the check-box via a Public Domain license. You can find it here:
I hope it will help you. Happy New Year!