In OS9, upgrade stuffit, then try a drag and drop rather than a double-click or Launch. If OS9 truncated the file name, you may need to retype the extension.

On OSX, click once on the file and Get Info to see the Open With options. THe file would fire up LimeWire if the Finder has the Open With setting wrong or you don't have the right app to open those files.

If it's a toast disk image, see if the toast menus allow you to mount it as a disk on the desktop (rather than make a copy).