epochonaut

I only used Dreamweaver once several years ago. Sounds like you might have to directly edit the source code and write a custom javascript function. If your checkbox has NAME="thisCheckbox" then you could write a javascript function like

function validateForm() {
if (document.formName.thisCheckbox[indexNumber].checked == false)
alert("You must check the box");
}

Can't help you with Dreamweaver though, sorry...