richard you are quite right that "ducting" as its refered to in the modding community does drasticly improve cooling performance. By gaining the ability to cool the CPU with the cooler air from outside the case thermal transfer can be achieved more readily.
you can see some commercial examples
here however they can just as easily be made with dryer hose. You can even buy newer cases with the ducts already in place however I've alwasy prefered to do my own on cheaper cases (if you have an Antec P180 you know better than to start cutting ).
Anyways this is an excellent fresh air mod however I would suggest filtering the entrance (some old pantyhose or used dryer sheet works great) to protect the cpu cooler from unnecesary dust.