What is Macromedia Flash Player Express Install?"Express Install uses the existing Flash Player to upgrade users to the latest version of the Player when it is required for viewing content. As a developer, this means that you have the ability to not only detect when users do not have the latest version of Flash Player, but you can initiate an update that securely installs the latest version of the Player from the Macromedia web site. When the installation is complete, the user is directed back your web site, where they can view your Flash content."
Some of you guys already knew this but Express Install FAQs are here