Case-Sensitivity with PHP and MySQL

I am writing a PHP script that operates on a MySQL database that uses the e-mail address as the primary key. If the e-mail doesn't exist in the database (when a form is submitted), I want to insert a new record. If it does, I want to update the existing record. How can I make the query that checks if the e-mail exists case-insensitive? I want to avoid users creating another record if they type in their e-mail in a different case. Thanks! rory ----------- providing the finest in midget technology