http://anandtech.com/weblog/showpost.aspx?i=630[quote:fa3c616d84] With the version of the Windows installer that comes with Win7, there is a new file at /Sources/ei.cfg that tells the Windows installer what OS it should install. Here’s what the file looks like from the ultimate disc:

    [EditionID]
    Ultimate
    [Channel]
    Retail
    [VL]
    0

 if you remove ei.cfg so that the Windows installer is not told to install a specific version, it will revert to One Disc mode.[/quote:fa3c616d84]