Delta Airline Pet Policies!!!?

Okay, I have a Shetland Sheepdog (Sheltie) and I need to know Delta Requirments. I've called the airline and the employee was no help. I am traveling first cl so the seats will be bigger. I need to know how big the carrier can be, about sedating my dog (yes or no), what happens if your dog can not fit under the seat infront of you, and anything else you can tell me. Please help, my trip is coming up very soon!!!