web form validation - random number

hi im using oscommerce [login to view URL] form hi i want to add a simple human verification into my web form. the idea i had was to have a RANDOM NUMBER generated each time the form is loaded and the person simply enter the number in the box before pressing submit, if they try to submit the form without the random number entered then it will not be sent or warning come e.,g Name: [enter your name] Email: [ your email address] Phone: [enter your phone number] Enquiry: [enter your enquiry here] Please enter the following Random Number in the box below: 3617 Random Number: [ enter the number shown i.e 3617] SEND/SUBMIT BUTTON NB: we can set it as 4 digits to start off and can change later in the code to 5 digits if necessary. We could also use letters. e.g abcd....xyz1234567890 as our "character universe" but im happy to try numbers only for now. im using [....] to denote an entry box above.