Why don't you zip or Stuffit the files and save yourself and your friend the hassle? Email the iso alone means sending uncompressed data, hope you two have broadband.
It is possible to make the iso, then compress it. If you don't want to pay for StuffIt deluxe, go on VersionTracker and look for ColdCompress (I think that's the name). It's basically a GUI interface for the built-in tar and gzip command line tools. tar.gz files are readable in Windows using WinZip.