uploading files | how to avoid submitting twice?

Hi there, I would like to upload files using a form. Unfortunatelly it takes a while till the file is uploaded to the server. During this time the same page with the submit button is viewed. If the user clicks another time on the submit button, I get wrong records and sometimes the same file twice. Is there a way to redirect imediatelly to a waiting page? I tryed to redirect, but somehow the server is first uploading the file before something else happens. Thanx for any help Andy