"Show Log" may be dimmed ("grayed out") in Disk Utility when started from the Mac OS X installation disk.
When you are started from the Mac OS X installation disc, Disk Utility actually sends its log messages to the Installer log. To view these messages, click the Installer window to bring it to the front, then choose Installer Log from the Window menu.
Note: In Mac OS X 10.5, quit Disk Utility to bring the Installer window to the front and view the Installer log.