After some time away from InnoSetup I'm back on that tool again to build some fairly complex Installers. Most of them need to check if .Net Version 3.5 is installed on the workstation the Software is installed. If .Net 3.5 is not yet installed the Installer should show a message box to the user right at the beginning and asking if he wants to download .Net 3.5 right now. If the user clicks "Yes" the Microsoft Download-Page will be shown otherwise the Installed will be canceled.