From what I understand after communicating with James at Inmotion...
Inmotion will send you the relevant cables etc. to hook up to your car (deposit required).
You hook it up to a laptop and they take some 'readings'.
They go away and 'write' new software for your car and email it to you.
You download the information to your ECU.

This way you are never without your wheels, which is a big plus if it's your only car. Check out there website for the details (basically requires a $2000 deposit which exclude the price of the tune).