[Memnoch]

OK, I found a way to fix the official plugin install problem from the Bethesda forums (from another user):

Step 1 Go to start, run, and enter the following command in then press ok control userpasswords2 then click on Administrator, and click Reset Password create a easy password for this, then press ok, this should close that User Accounts window. Step 2 copy the exe file of the plugin into C:\Documents and Settings\Administrator\My Documents Step 3 run the exe plugin, by rightclicking it, and choosing runas. Click the button that says "The following user, Select administrator and enter the password you made before. Walla, it does the activation, then installs it no problems Step 4 (Backing up) Go to the following directory C:\Program Files\Bethesda Softworks\Oblivion\Data and copy all files with DLC*.* and the DLCList to a backup area, this will elimate going through all that process again, if need to reinstall.