Hi,
Not exactly sure what you mean. I guess you can trip the INT0 interrupt "internally" simply by setting the interrupt flag so in that sense they are available internally. But what is meant by external is that the event causing the interrupt is being external to the PIC itself, ie an event on the physical pin. In the case if INT0 (which is usually on PortB.0) either a rising a falling edge depending on how it's setup.

/Henrik.