[dnanian]

No problem -- that's a bit of an advanced option: sorry if it's unclear.

This can be used to install a package, such as a standalone system update. For example, Mac OS X 10.3.3 comes, sometimes, on a DMG, rather than through Software Update. By mounting the DMG during the Safety Clone process, you can tell SuperDuper! to install the package that's on that DMG (the icon looks like a "package" -- it's a special bundle of files that's used by Apple's Installer program), you can save a teeny bit of time.

For most users, though, this is something you can safely ignore. Instead, you'd create the Safety Clone, boot from it, and then just run Software Update when you're booted from the Sandbox: Software Update will automatically download the "package" and install it.

Hope that helps to explain things a bit.