Secondly why use a IGBT?
Your current design is guranteed to lock up and you may as well go back to the drawing board.
dc42, thanks for the diagram. I found a IRF5210PbF which has a pulse current rating of -140A which is more than 15x my 8 amp steady current draw.
I have done some forum searching and this thread (http://arduino.cc/forum/index.php/topic,62503.0.html) recommends using a "TC4429" mosfet driver. It has something to do with the mosfet not switching cleanly with a transistor. Would this be better? What do you think?
The 1k resistor can be reduced, indeed, but the 10k resistor is sensible - it stops the MOSFET gate floating when the Arduino is powered down.