there is some confusion as to what you want and I suppose we have a language barrier.

I currently have timer0 setup as a counter (external counts on T0 pin) and also setup so that when the counter overflows it jumps to vector 000Bh to increment an upper word register to make a 32bit counter. All of this works perfectly !
so far, so good

Now what I would like to do is every time the T0 is activated, I would like to check the status of a bit and turn it on if it is off. The only problem I am having is I cannot find the vector address for Timer0 so that I can add the code to check that bit every time the T0 pin is activated on the processor.
do you want to
a) just know when the pin toggles
b) keep T0 as a counter AND know when the pin toggles
also
c) what is the shortest time (microseconds) ever between two pulses
d) how precise timewise do you need to turn that bit on and off
e) what exact chip do you use
f) what is your clock speed

Answer this and till you do there are way too many suggestions.

Erik