Help with JavaScript

I am coding a web site for class that requires me to validate two fields in a form against the current date: the credit card expiration month and year. I have them both listed as drop downs with the months listed as 3 letter abbreviations and years ranging from 2004 to 2009. As I have written approximately ZERO JavaScripts before in my life, I would appreciate any and all help. The URL to the site is here for those interested.

I have coded :

<script language="JavaScript1.1" src="CreditChecker.js"></script>

function validateCredit(form)
{
return (
checkString (form.elements["CCMonth"]) &&
checkString (form.elements["CCYear"])
)

}

</script>

thusfar and need to figure out how exactly I am supposed to get this to be checked once the user hits the submit button (which is also inoperable at the moment, but I think that the two will rely on each other in the end).

I made the initial form in FrontPage after having my butt handed to me on a plate when trying to work with DreamWeaver . I'd assume that DW is much easier once you have at least played with it for more than an hour or so. Plus I am not willing to bring my copy of DW to work so that I can hand over the license to my boss, so I talked him into letting me install FP.