My American house was built in 1942, and much of the wiring is still knob-and-tube wiring (2-wire, no ground). Over the years new modern wiring has been added to the house, but we still have some KnT wiring for the ceiling lights, and a few branch circuits, etc. We are planning to replace the KnT wiring when we have the budget to do so. I have replaced many of the receptacles on the KnT circuits with GFCI receptacles to provide added protection, which is recommended. 

I have seen [AFCI and GFCI circuit breakers](http://www.homedepot.com/s/afci+circuit%20breaker?NCNI-5) which plug into the service panel, and they are reasonably priced at $30-50 per breaker). Would these AFCI or GFCI circuit breakers provide any protection on old, knob-and-tube wiring?