I take if from your post that you wish to uninstall Microsoft Security Essentials and install Forefront in its place. Is that correct? To do so you will need to uninstall MSE. If you cannot uninstall using the automated method you can use the advice from
this link for any version before version 2:
http://support.microsoft.com/kb/2435760 . Having uninstalled MSE you can proceed to installl Forefront. I would recommend downloading the installation pack afresh if you are missing files. I would also check that you don't need to install additional software
or updates in order to facilitate installation. If so install all of these before you try to install. The system requirements can be found at this link:
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