Commerce

I have a website where I sell my products (software application). I offer free small test/demo on-line. What I want is to offer entire software (interactive tests) on line for the customer; so, I will not have to send him/her the CD-ROM. User will have to pay first, to log into my server and use my product. Some security must apply; I do not want people upload it to their hard drive and copy it. I am looking for someone who did similar project in the past and has experience in this. I like to have few levels of access (brown, silver, gold, all with limited time access). There are more requirements but it will be a second project following this one.