Private Sub Timer1_Tick(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Timer1.Tick
        If Not httpclient.IsBusy Then
            index += 1
            if index <= maxindex then
               Dim Link As String = .....(index)
               Dim sLocalFile As String = ........
               httpclient.DownloadFileAsync(New Uri(Link), sLocalFile)
            else
               timer1.Enabled = false 
            end if 
        End If
   end sub