I\'m writing an iPhone app which downloads a tar-gzipped file from a Webserver, then needs to unarchive this file so that it can be copied into the app\'s Documents folder.<
This blog post should help you:
http://blog.hawkey.org/?p=332
EDIT: Google cache version of the same page which actually links to a forum post here which links to a Google Code project here, containing some code which implements unzipping on iOS.