There are two versions available on DVD, the MGM version which is widely commercially available, and the IRE version, whose transfer was commissioned by Godfrey Reggio for its pressing to DVD, several years before the MGM version was announced. The differences between the two versions are that the MGM DVD is in anamorphic widescreen, but bizarrely the IRE version, which is in fullscreen (4:3) resolution, gives a much greater view of the images. There is much debate as to which version was seen as the intended release, but regardless, this IRE DVD is an amazing version to watch if you are a fan of the film.
Check a comparison here and here. As you can see, unlike the majority of 4:3 versions of films, the IRE version wasn't cropped to get it to fullscreen, but in fact was done the opposite way where the MGM version was cropped to get it down to its widescreen 16:9 aspect ratio. The IRE version is also sharper and better quality (with a higher bitrate) than the MGM release.
The IRE version was released as a very limited release directly from Godfrey Reggio a few years before the MGM version finally came out on DVD, at a time when it wasn't sure if a studio was ever going to release it on DVD. This release via Godfrey Reggio's website was very very limited though and is loooooong since unavailable (except via eBay for over $150 per copy). Consider this a preservation commissioned by Reggio when it didn't look like any other DVD release of the film was due to happen. Now that MGM have released their version, the IRE version has been relegated to the same world as pre-commercial DVD bootlegs, it just so happens that the IRE version is better than the proper commercial release!
Sooooo, for you preservationists and fans of the film, this IRE version is an extremely interesting and enjoyable version to have. A torrent of the IRE version is up and available to snag from torrentspy.com (search for "Koyaanisqatsi_IRE"), and is currently being seeded, so if you are interested, jump on it and get downloading (but please remember to seed this as long as you can once you've completed the download).
I'm just the messenger, so no credit goes to me for the rip/preservation of this DVD, the version available via BitTorrent is a straight 1:1 copy of the DVD distributed by Reggio, seemingly no re-compression or alteration has been applied as the original happily fitted onto a DVD5 disc.