Hi,
What "type" of interrupt are you using? ON INTERRUPT, DT-INTS or "true" ASM interrupts?

By the sound of it you're using DT-INTS in which case my guess is that you can't GOSUB to the handler because the handler doesn't end with a corresponding RETURN (the @ INT_RETURN is not the same thing as a "normal" RETURN) which makes the PIC go off to la-la land.

Have you tried, after enabling the interrupts, to simply write to the corresponding interrupt flag bit? I've never tried it my self but I can't se why that wouldn't trip the interrupt. For INT0, simply try INTCON.1 = 1

/Henrik.