agree agreement buttons buy check checkbox checked cheers click click-wrap contacted customers customize deal example feedback licensing point present proceeding process seller selling shrink-wrap user welcome

Hi,
I'm about to start selling with e-junkie and I need our customers to agree to our End User Licensing agreement. You know, it's the check box that you have to click before proceeding - often called a shrink-wrap or click-wrap agreement.

I've contacted E-Junkie and they have said that it's up to the seller to deal with the click-wrap agreement. So, I'm curious about your process. If you have one, at what point do you present the agreement? Do you customize the "Buy" buttons to not be live until the checkbox is checked? Any thoughts/feedback are welcome. Any example you can point me to? Cheers!