For keeping a track of cd-keys added, you could link a text file, and ask the user to register a username, and that username will be used to obtain their keys.
Keep a list of users in a MySQL DB and make two PHP files, one to register and one to login. Make one get request on the register one, and make the script save the input to a text file, and for the login, just make the web server ask the script if that text file contains the input into the get request.
For the Visual Basic side of things, you can do that, there is no need for me to explain that to you.