Duplicate entries

first off, I am very impressed with this service.

I have a database of names, phone numbers, email addresses, etc. the database is pretty sloppy an missing some information for some people. I want to have everyone reenter their info through a form and have it overwrite the fields if it is a duplicate. for instance, if the first and last name on the input are the same as that already in the database it would not create a new line, it would fill in the empty fields(or overwrite the existing) with the new info. is there a way to do this using scripts?

Thanks
jlongton