Hi,
please could someone point me in the right direction:

I have a mod. which looks at the postcode and decides if a customer is entitled to free delivery.

My users are putting their postcodes in the format "po175nd".
The expected (and correct) format for a postcode is "PO17 5ND".
How do I validate the postcode field for new customers so that they enter their postcode in the correct format?

(Please be gental with me: I have some HTML and JavaScript, but not much!).

Many thanks,
James.