Simple File Joiner Pro allows
you to resize the application
window and pass in a list of
files to be joined via the
command-line. Simple File
Joiner works on text files,
some movie files (like mpg
movies that are all the same
size and encoded the same, but
not with avi files), and
others. if the files you are
trying to join together each
have header information that
pertains to that particular
file, SFJ will not work. This
includes GIF, BMP, JPG, AVI,
DOC, etc.

http://www.peretek.com/sfj.php