Postcode check help

[bob33]

Hi,

 

i`m trying to put a put a postcode check in the site layout, eg: http://www.cosmicuts.co.uk/example.jpg

 

I have no idea where to start with the code, but would like in a way that i could input true and false values, eg if it contained "sw19" or "SW19" value = true. If postcode is something not listed, value = false

 

also True and False results will take the person to a relevent page, or relevent pop up a box.

 

Thanks for your help, I've been trying for the last few hours to make something thats even close to working, but totally stuck