I have inserted the "using 1" line code in the ISR. But still does not do anything. What about if "using 1" has been used for different ISR. could I use it again? could I use "using 2" instead...in other words how many times can I use the same register in ISR's.
I use one level of registers for each interrupt priority since interrupts of the same priority can not interrupt each other (see "the bible")
Also, I have noticed the TF0 bit does not get set after overflowing...therefore, ISR is not executed. Why?
Ah dunno, your code seems ok. Try creating the code using
http://www.codearchitect.org/
and compare the result, that may tell the story. Once you find out DO come back to the edification of the rest of us.
What do you mean by have I looked in my emulator?
Well, evidently you do not have one and must use other debugging techniques since you know that TF0 does not get set.

Erik