.dmg's are Disk iMaGe files for OSX (I'm guessing you are on OS 9)

There are too many formats to list easily here. See http://www.gnutellaforums.com/showth...threadid=25521 for a link to a good page explaining extensions, or just search these forums for "rar"

btw--stuffit expander and quicktime have checklists of extensions suitable for your Mac in their Preferences. That might be the easiest way to see what internet file types to look for.

cheers