See <http://docs.info.apple.com/article.html?artnum=58583> and especially note: "Using Target Disk Mode with Intel-based Macs If you attempt to mount an Intel-based Mac in Target Disk Mode on a Macintosh running Mac OS X 10.3.9 or earlier, you'll see an alert message." For more information, see <http://docs.info.apple.com/article.html?artnum=303118>, "Intel-basedMacs: "You have inserted a disk containing novolumes that Mac OS X can read" alert message"