how to remove the particle board subfloor underlayment quickly?
Buy a cat's paw prybar and pound it under each nailhead, pull each nail individually. I know it sounds painfully laborous, but believe me - much cleaner, efficient, and productive. Make sure to test the smallest piece first - they may all be glued. If that's the case, go buy the cheapest latex paint you can find and paint over the floor to seal in the stink until you get your carpet.

Honestly, I'd call my latter suggestion "Plan A", but I don't know your situation.