sleestack how large is the rar file u are trying to open?
have u tried to inspect its properties to find out any information ie: the original app /os platform that was used to compress it to RAR format?
you could always expand the .rar files on osx,
and then use an osx app called "dropDMG" to create a new .img file (os9 compatible)
and then you can easily drop to terminal, and issue the following command to encapsulate it as a .bin file for safe transfer to os9 machines
"macbinary encode -v FILENAME.EXT"
this will create a img.bin file from OSX that is 100% compatible + safe for transfering over the internet + back to any macos machine
maybe that is above your skill level ? its really easy once u do it once