jQuery Validate -- if "other" checked, require input box

I have a “How did you hear about us?” with a series of checkboxes that is working great, however there is an option for “Other”, where they can fill out their answer.

I want to modify the script so if the checkbox for Other is selected, they are required to fill in the input box.

I have this working here, but I cant get the input box to be required if “other” is selected:
http://psylicyde.com/misc/jquery-validate/demo/test.html

I’m still working on this and Im getting there but Im having a hard time with the syntax of a function in jQuery. In the commented code below, I tried to write it out… if the checkbox “other” is selected, I want to require the refferrerother text input box…

$().ready(function() {

	$("#signupForm").validate({
		rules: {
			referrer: {
				required: true,
				minlength: 1
			},
			referrerother: {
					// if referrer('#other').checked require refferother
					// how can i do this?
					required: "#referrer('other'):checked",
					minlength: 1
			}	
		}
	});
});

Found an awesome example for this here:

http://www.coldfusionjedi.com/index.cfm/2009/2/16/jQuery-Form-Validation-with-Selects