I agree with Scott. The kid needs to be ready or it's not going to work out.
Our daughter Savannah is five. She was trained before our son was born, when she was 2. It was her idea, and pee was easier than poop. We actually bought a doll as a "reward" to get the ball rolling. The doll was put on a high shelf, and the first time she was successful on the toilet the doll came down. If there was an "accident", the doll returned to the shelf until the next time she was successful, which usually didn't take long.
She still wears a pull-up to bed, and had an accident on the couch just yesterday when she fell asleep there.
Our middle son Leif is 2 1/2 and shows no interest, so we've left it alone with the new baby coming because we didn't want to deal with a regression. I'm planning a lot of time spent in the yard with him this summer, no diaper, tied to a stake.
Obviously, the 2 week old Finn is still working on the concept of indoor plumbing.
Where are you at in the process?