Creating a PWM signal using PIC18F4520
You cannot get a 100ms PWM period with a 20MHz clock. The maximum will be something like 16ms. You can run the micro slower or use a faster period. Generally the period is not too important and you want to maximize the resolution. 

Please read the datasheet and reference manual sections on the timers carefully, there are too many issues with your understanding.

Also note that you have confused 0x31249 (201289 decimal) with 31249.