starter replacement?

On the front of the engine.

On a 1998 cadillac seville I can turn on the air conditioner on 65 degrees and the passenger side cold air comes out but on the drivers side , heat comes out. What could that be?

Stuck or non-actuating diverter or blend door. Make sure all electrical and vacuum connections to the air box are secure and not leaking.

On my 2001 cadillac deville, the front brakes were squeaking, and I replaced them and put the squeak grease on it and they are still squeaking, why?

Dirt between pads and rotor. No non-directional swirl finish on the rotors. Sharp edges on the pads catching the machine grooves on the rotor. Loose parts.

I changed a starter on a 2000 cadillac seville and I have had to take the injectors out, I have replaced four of them and the o-rings, and it smokes like crazy, why does it do that?

either because you did something wrong, it has bad rings, bad valve seals, or a leaking head gasket.

On a 1998 cadillac seville the service engine soon light is on and I have a OBD2 computer and it reads PO340 camshaft position sensor circuit,and I have replaced the camshaft position sensor 3 times and the light won't delete, it keeps coming on,so is a camshaft position sensor circuit the same as a camshaft position sensor or what else could it be.

The circuit is the wiring. The sensor is the sensor. Check the wiring and the connectors.

On a 2000 cadillac seville the service engine soon light is on and the code says PO174 Fuel trim system lean (Bank 1). What does that mean? How do I fix it?

On the same car if the fuel from the fuel injectors leaks into the intake manifold will that make the car smoke like crazy?

It means the air fuel mixture is incorrect.
In order to get the fasted replies, you should create a new thread/question for each question. That way more people will see it as needing help. I'm guessing that a few of my colleagues have begun to ignore this thread.