If you are planning on using Target Disk Mode to boot your Mac equipped with Thunderbolt ports you’ll need Apple’s special Thunderbolt cable in order for it to work. This is required even when connecting two Macs or a Mac to an external Thunderbolt equipped disk drive.
Currently only the 2011 models of the MacBook Pro and iMac support Thunderbolt, but Apple is expected to refresh the remaining models like the MacBook Air soon. You also need to make sure that you are running Mac OS X 10.6.8 and you will also need to install the Thunderbolt firmware update that Apple recently released.
Once you are set up with the proper equipment, OS and firmware updates, and the Thunderbolt cable you are ready to go. You can check out this document for generic information about Target Disk Mode on your Mac. Although this document details Target Disk Mode for Firewire the same steps work for Thunderbolt.