recover data from corrupted tarball

[e-letter]

Readers,

A tar ball was received, created in m$ environment using 7zip. Using
gnu/linux mandriva (m$ not available) The normal tar extract command
was applied:

tar -xf ...

which was unsuccessful, returning command terminal response:

tar: This does not look like a tar archive
tar: Skipping to next header
tar: Error exit delayed from previous errors

Using the tool 'file', the tar files are classified as 'data', of
mime-type 'application/octet-stream', which I presume means that the
the tar ball was formatted in error to some binary format.

Any advice to obtain the files in the tar ball?