Hi Lynne,Microcreations might work. The best thing to do is to contact the creator of the program. In the past several people have tried to contact the creator of MC without any luck. Email him first.
Since you're selling on Ebay you might like to look at this PayPal Instant Payment program, which provides a temporary link to your product after a PayPal payment.
http://www.vibralogix.com/linklokipn/
The problem using a program like LinkLok is how to provide the password for unlocking the ebook. The most practicle solution (without a lot of programming) is to include information on sending the registration code to you and you will send them the password to unlock the password.
If you are comfortable with databases it is possible to write a program that will tie the password, registration code, and the user's password together. By tying the password and registration code to the user's email allows a system where the user can query the system and have the password emailed to them.