You don't need a new button to do this. You can use the function "PreSaveAction()" to handle form validations, confirmations, etc. after the user clicks the normal save button on the form. SharePoint forms will recognize the PreSaveAction() function and wait for a return of 'true' from that function before it commits the data and closes the form. If your result returns 'false', the form processing stops after the PreSaveAction.
Geoff
Geoff