Depending what your site is offering, you may want to give an option for a user to select a "code" that they can enter to automatically fill in their name and address.

This of course assumes the user has some reason to fill in address information with some attempt at accuracy.

Just some thoughts on how dageek might try it. try to create some standardized wording. Split on white space, replace MD with DR in name fields (you will build a list of others). In the Address fields, replace NORTH with N., South and So with S. and so on.

Now compare for exact match for words and numbers.

Store "standardized" name and address in main database for future compares.

You have a good piece of work ahead of you no matter what method you choose - Good Luck!

dageek