Just to add one more voice to SJ's
Don't do it! The regkey will be illegitimate, ultimately you'll get burned.
I realize your budget's pretty thin right now and I don't wish to lecture, but $39.95 is dirt cheap for software as good as this, combined with lifetime ownership and upgrades. A purchase from an unauthorized 3rd party not only would be unethical, but Fengtao and his team have to make a living too. Overall it's a darn reasonable price.
You're probably already using DVDFab Decrypter...it's freeware and updated routinely. I'd keep using it and save your pennies.