Uncompress (zlib) files that "S3 Backup" compressed to Amazon S3
To help figure out what these files are compressed with, you can try using the file command from the terminal. It should give you output like this:

% file archive.zip 
archive.zip: Zip archive data, at least v2.0 to extract
% file archive.tgz 
archive.gz: gzip compressed data, from Unix, last modified: Wed Aug  3 06:21:00 2005, max compression
% file srchive.bz2
archive.bz2: bzip2 compressed data, block size = 900k