Calvin
The way MS does it is to distribute a printed reg number with each copy. After installation, the user can use it 40 times before shut-down and there is a nag-screen so they get lots of warning. after 40 days is up the trial is over and it shuts down or they register and pay. When they register, you've got all previously registered reg numbers in your database so you'll know straight away if somebody is trying to reuse a license.
You could easily create a reg scheme along the lines of 1E232-E4666-J1788-BCVLX where some of those characters are random, some come from a position lookup based on other characters, some are a checksum (so people can't invent a reg number).
Invest in Konxise as well to make it harder for hackers to get your algorithm and offer it around.
If you do it this way you can still use your current protection mechanism on top.
Regards
JR
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
