Target Disk Mode(for Mac Only) Using a 6-6pin Firewire(1394) Cable. You can connect A Mac to another Macs Hard Drive. Pin6 Firewire is std on all G4, G5 and Intel Macs.
You can connect through the Firewire Port to access another Mac's Hdd.
Press and hold T during Startup of the Mac whose Hdd you want to access, a FireWire logo appears, then connect the cable to both macs Firewire port.
Startup the 2nd Mac if its not already started up, a ext drive logo will appear on the desktop ready for access.
This TDM can be a great troubleshooting tool, to start a Mac from another Mac, access the Hdd of a Mac that doesn't fully load into OS X, etc.
Search "Firewire" to get the cable. Try it, it's fun.

This method is also how you can connect your old Mac to migrate to the new one using "Migration Assistant"
Hope you found this useful. Thanks