Ok, I threw this page together after running into a .7z file. I used this linuxquestions.org post and this Arch forum post to put it together. Then, when searching the Arch wiki to see if I needed to make any redirects to catch searches for the file type, I found this page and saw the 7z command in a page called Core Utilities and thought it must be one of them. Further search revealed that is incorrect, and that p7zip IS needed to open these files. As far as I can tell.
I'm just a beginner, but I felt a page on this would help, so I put it in place to the extent that it would have helped me, and I hope that anyone who knows more will correct any errors I make. Stevepoppers 08:22, 2 June 2011 (EDT)