My experience is that if you have already some programming skills, it is pretty easy to switch from one programming language to another. You just have to get used with the new syntax.
To quickly get used to the basic of some language, you can try following some simple tutorials. There are plenty of tutorials on the net, ranging from programming a blinking led to much more complex stuff.
If you would decide to use C18 from microchip, **broken link removed** is a tutorial that explains everything you need to know, from setting up a project to effectively programming a simple program on your microcontroller. Although the tutorial assumes that you use the popular PIC18F4550, you can also use a different microcontroller, just pick the right microcontroller when setting up the project.