<p>How do I learn PLC programming? Would it differ greatly for different brands of PLCs? Is ladder programming the same as PLC programming?</p>

PLC is the term used for the devices that use ladder logic.  The devices that are programmed in more typical programming languages are generally called microcontrollers.  However, there are some of us that on occasion lump them all under the PLC name.  :-)  Not sure how much ladder logic varies, but microcontroller code can vary significantly.