Quoting grelber:

"The new iMac has a FireWire 800 port, whereas my current machine has an older FW port."

If your old iMac supports FireWire it seems likely that it can boot into FW target disk mode.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire