The trick here wouldn't so much be the 'untarring' part, since you could use tar.gz and both Unix and Windows users (with WinZip) could extract it.

Maybe what you could do is create an archive containing another archive with the main program in it and a Perl script wich will interactively install the other archive to a directory of the users choice. This would actually work well too, because you could have the script check the environemtn, permissions and module availability on the machine as well. It's an extra step, but no worse than downloading any install files and then running the installer/rpm/etc.

-- I'm a solipsist, and so is everyone else. (think about it)