To start with by using DT instant interupts the interupt will be performed no matter what the PIC is up to for the moment.. The PIC will stop in it tracks, do the interupt, toggle the led, return and then comtinue off where it was before.

First you wanted to flash a LED to show a busy task, now you want to fade a LED....

Is that one led or 255 leds or fading while doing other stuff..... I think I speak for more people than myself when I say "hmmm confused"..

What have you done previously, how much do you know about the PIC HW and what will your project do when it is done?

Good luck and I will keep an eye on this thread to see if I can help later on