Click the Eject or Ignore buttons to dismiss the dialog. Mac OS X 10.3.9 or earlier cannot mount volumes from an Intel-based Mac in Target Disk Mode.
However, if a computer running Mac OS X 10.3.9 or earlier is connected to an Intel-based Mac and started up in Target Disk Mode, its volume(s) appear as expected on the Intel-based Mac.
Format Intel-based Mac's startup volumes only from another Intel-based Mac
If you want to format an Intel-based Mac's volume(s) while it is started in TDM, and you intend to use the formatted volume as a startup volume, be sure that it is connected to another Intel-based Mac, then use Disk Utility to erase the disk before you repartition the drive.
Important: If you format the Intel-based Mac's volume using a PowerPC-based Mac, Disk Utility will successfully format the disk but you will not be able to start the Intel-based Mac from it.