noob problem - Conditional hiding.

[matty321]

im new to all this but basically my problem is:

in a box i have a drop down list with the 2 payment options, cheque, and credit card. what i want to do is when i have cheque selected there are no boxes but when i select credit card, a few boxes will appear for things like credit card number, card holder name etc.

basically, could someone help me write a code or forumla, and give me help in where to put it as i have no idea

thanks

matty