Program Download Key Generator

My client has 2 pieces of 30 day trial software that he wants to make available for download. But he wants the customer to input their information in order to login and get the file, so he wants some sort of validation process whether it's validating the zip code or email address to confirm that the information is valid. The second part is that once they're logged in, the system will generate a key that will give them the ability to download the software. This key needs to either expire after 2 uses, 24 hours, or some type of time limitation. He doesn't want the customer to be able to download the software multiple times. I know that osCommerce has the download purchase capabilities built in, but osCommerce is overkill since he only offers these two pieces of software. Additionally, because it's free trial software, osCommmerce doesn't have anything in place to keep the file from being downloaded multiple times and abused. Essentially he wants to offer this software to customers but wants to verify their information somehow when they login and also wants it to generate a key so that the download is ony good for that customer only and limit them to one download (unless the download fails midstream, then they can download it again, which is why I said maybe 2 downloads). If we can limit it to the customers IP address or something that would be fine. I won't consider anyone who doesn't offer me a rundown of their solution to how to do this. If you just say "I want the job and we'll do it", you WON'T be considered. I want to know how you plan to do this. The one who gives me the best answer, has good feedback, and is the most cost effective wins this project.