preventing multiple submissions

I have a problem with a form on my website. it's part of a shopping cart application, whereby the form consists of a list of products and the user enters the quantity they require of each product in the field provided. Everything works okay except for the fact that if someone hits the submit button more than once the products will be added to the 'cart' more than once. I've tried altering the script that handles the posted form info, but the problem persists. I've also simplified the page that loads after adding products to the shopping cart so that it loads quicker (people are less likely to click the submit button more than once). Can anyone suggest a solution? Thanks in advance for any help. Regards, Derek ********************************************************************************** This e-mail (and any attachment) is intended only for the attention of the addressee(s). Its unauthorised use, disclosure, storage or copying is not permitted. If you are not the intended recipient, please destroy all copies and inform the sender by return e-mail. This e-mail (whether you are the sender or the recipient) may be monitored, recorded and retained by Business Information Publications Limited (BiP). E-mail monitoring/ blocking software may be used, and e-mail content may be read at any time.You have a responsibility to ensure laws are not broken when composing or forwarding e-mails and their contents. **********************************************************************************