my suggestion would be to go completely back to basics.
Do a backup of your complete exisitng database.
Then install the user registration package as per the WA instructions - which do work-.
Then run the registration package and make sure it all works out of the box.
Once you have proved this you know that the package works and your php mysql setup is compatible.
I'd then re instate your database and check that none of the tables between the two have the same name.
It is then just a question of running the sql statement on your exisitng database and filling in the connections details.