I don't know how my 2006 F350 was maintained. Having bought it used, where would I need to start to get it ready to be put into service? Do I need to put a chip in the computer?

So you bought a truck with a 6.0 that you never saw running?

THe 6.0 has a history of problems, if you never saw it run it could be any of them... none of those were computer related to my knowledge. I'd have a qualified diesel mechanic give it a going over.

I assume you have the key...

Yes. I was told that it needed a new ECM.

Well the ECM is the complete computer... not just a chip. Newer vehicles woud need a reprogramming on an ECM replacement to match your VIN etc...