address info, forms, maintanance

I need to modify some company web pages that include a form for asking the company departments questions, such as service dept, etc. As the forms are currently built there is some field validation but no cookies. This info is saved in a mysql database, problem is, there are duplicate entries, every time an end-user posts a question. What kind of code do I need to add to these existing pages to prevent duplicate entries in the database? (Manually scanning through and deleting dupes is a real drag.) And what about cookies? Could I make use of these on these pages? I haven't worked with cookies yet, so am not sure where to start with that part. Thanks, -- Chip