Hidden Form Fields

i wrote a script in asp/vb script that validates form fields. all works fine, apart from the fact that alerts are being shown against the empty form fields when the page loads the first time.

so, validation should not be carried out when the page loads the first time. my friend challenged me and said i can achieve this "using a hidden form field or even the submit button" and submitting the page to itself

i was more thinking of using session variables or a session cookie, but does anyone know how you could accomplish this using a hidden form field?