In addition to ".sit", you can also try ".dmg"


ADDED NOTE:Macintosh Users:

Correct me if I'm wrong, but trying to share a DiskCopy or ShrinkWrap ".img" or ".smi" file through Limewire could be absolutely pointless.

The ".img" file format, as well as the ".smi" self-mounting variety, each contain a small amount of critical resource fork information. It's possible that this info won't be preserved during the download. This is because Wintel boxes (which could handle the file somewhere along the line) don't understand what a resource fork is, and will consequently sever the file. They can only understand, and thus preserve, the data fork. The end result will be a corrupt disk image file that won't mount.

If you want to share a ".img" or ".smi" file, please be sure to encode it in order to preserve the resource fork information. In other words, before sharing, convert it to a Stuffit Archive file (".sit"), or encode it into a MacBinary (".bin") file or a BinHex (".hqx") file. Alternatively, if you're using OS X, you could create a ".dmg" file.

Thanks....and keep sharing!