Pacifist lets you extract or install the contents of package files, such as this package file on the iWork ’08 installation DVD.

I recently bought iWork ’08. I put the DVD into my drive, but when I double-clicked the installer, an error message said, “No default application specified to open the document iWork08.mpkg. Choose application.” Why can’t I install this program?

The iWork installer that you were double-clicking is actually a MPKG file (meta package file), which is a set of compressed files that require Apple’s Installer application to unpack them and install them on your hard drive. The Installer application comes with Mac OS X, not with the software DVD that you bought.

In Mac OS 10.4 (Tiger), the Installer application is located in /Applications/Utilities, so if you’re using 10.4, you may have accidentally thrown it away if you didn’t think it was necessary. In Mac OS 10.5 (Leopard), Apple moved the Installer application to a more hidden location at /System/Library/CoreServices, to make it less likely that people will accidentally move or trash it from there.

If you’re missing the Installer application, your best bet is to reinstall Mac OS X—this will make sure that you get your Installer back, plus any other important system files that might be missing as well. If you already have the Installer application on your Mac, you may need to use a tool like Cocktail ($14.95, www.maintain.se) to rebuild your Launch Services database, which keeps track of applications and their file associations.

Alternatively, you can use Pacifist ($20, www.charlessoft.com) to extract or install the contents of any MPKG file, such as the one on your iWork ’08 installation DVD. Pacifist can also extract files from PKG files, DMG disk images, ZIP files, and more.