How can I create a .dmg disk image for Mac OSX ?

A common way to distribute Mac OS X installers is using a simple ZIP file that will be uncompressed upon download automatically. However, there may be situations in which it may be desirable to provide a Disk Image (DMG). Currently, BitRock InstallBuilder doesn't provide a built-in feature for this. However, you can create a .dmg from the command line using the hdiutil OS X utility.

Here are two articles describing how to do it:

http://www.macosxhints.com/article.php?story=20020311215452999

http://www.codejedi.com/cgi-bin/blog.cgi/technology/apple/20050814making_dmg.blog

It is also possible to create the DMG images from Linux with a little bit of work:

http://www.trampolinesystems.com/blog/machines/2008/05/19/creating-dmg-files-without-macos-x/