Hello,
First, what is TDM? Targeted Disk Mode.
Back in the day of the first Mac laptops, and I think it was System 7, you could take a Mac laptop that had a special SCSI Cable (it was missing a pin) and using a control panel setting, turn that laptop into an external SCSI hard drive. It was very neat and convienient for moving large amounts of data, especially since a lot of these laptops (such as the 520, 5300) did not have a built-in CD-ROM, nor a built-in ethernet connection.
On Today's OS X machines, you can do something quite similar with Firewire. You will need a 6 pin firewire connector with the proper connectors on each side. All you need to do is wire the computers together with the cable, and then reboot the laptop while holding down the letter T on the keyboard. Feel free to look here for specific information:
http://docs.info.apple.com/article.html?artnum=58583
Firewire also supports IP, and if you are trying to do TDM from a Windoze, box, you might be interested in this:
http://www.macosxhints.com/article.php?story=20031112091634533
I do not have modern enough hardware to test this out.... I am still a SCSI shop with my G3. The old way still works for me under OS 9 and SCSI.... and those of you working with SCSI, remember it is not hot-swap!
Let us know,
Christian