Problema al Deshabilitar Boton en Formulario

[carlosfocus]

Saludos

el formulario antes de enviarse pasa por una validacion de campos y el codigo es el siguiente

<SCRIPT LANGUAGE="JavaScript">
<!-- Begin

function validate() {

var theMessage = "Please complete the following: \n-----------------------------------\n";
var noErrors = theMessage

// make sure field is not blank
if (document.form.nomb.value=="") {
theMessage = theMessage + "\n --> FIRST NAME";
}

// make sure field is not blank
if (document.form.apellido.value=="") {
theMessage = theMessage + "\n --> LAST NAME";
}

// make sure field is not blank
if (document.form.empresa.value=="") {
theMessage = theMessage + "\n --> COMPANY";
}

// make sure field is not blank
if (document.form.direccion.value=="") {
theMessage = theMessage + "\n --> ADDRESS";
}

// make sure field is not blank
if (document.form.ciudad.value=="") {
theMessage = theMessage + "\n --> CITY";
}

// make sure field is not blank
if (document.form.telf.value=="") {
theMessage = theMessage + "\n --> PHONE";
}

// make sure field is not blank
if (document.form.mail.value=="") {
theMessage = theMessage + "\n --> EMAIL";
}


// validate an e-mail address
if (!/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,4})+$/.test(document.form.mail.value)){
theMessage = theMessage + "\n --> Enter a valid e-mail address";
}

// If no errors, submit the form
if (theMessage == noErrors) {
return true;

} else {

// If errors were found, show alert message
alert(theMessage);
return false;
}
}
// End -->
</script>