Linux's tar makes relative tar files by default.  That is, even though you
say tar -tvf /etc, what you get in the tar file are relative path names,
e.g. etc/passwd, not /etc/passwd.  To override this, use -P.

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Tar files with a bz2 suffix use the bzip2 (compression/encoding?) scheme.
Use the -j option with these files, e.g.
   tar -jxvf some.file.tar.bz2

Some of the Open AFS came in this way, e.g.
  openafs-1.2.11-doc.tar.bz2
  openafs-1.2.11-src.tar.bz2