I'm assuming you mean 7Z. This is a file extension used by the compression software 7-Zip, which you need in order to unpack the 7z file. It's free, and you can download 7-Zip from the following link; http://www.7-zip.org/ The 7z file you download from the nexus will actually contain one or more of the true files you need to install, but in a packed format. You therefore have to unpack them (using 7-Zip) before you can install them. It's an easy process. People do this because the package is a lot smaller than the loose unpacked files, so it's faster to upload to the nexus. Hope this helps ;) Unfortunately I have tried several times to download the 7-zip file archiver and keep getting an error message: "The installer you are trying to use is corrupted or incomplete. This could be the result of a damaged disk, a failed downlaod or a virus. You may want to contact the author of this installer to obtain a new copy. It may be possible to skip this check using the /NCRC command line switch (NOT RECOMMENDED). I have tried several times to download it and get the same error every time. I am hesitant to end up with a screwed up program on my computer... Already have too many of them now LOL