You have the bike all set up for riding? You should really ask yourself if all this hassle is going to be worth it. At the end of the day, if you do choose to get your fork threaded, you will have to get a threaded headset too.

Threading a fork: $35 or so
Headset: $25 or so
Installing a headset: $15 or so
Initial cost of Nitto Tech stem: $30 or so

You are in the neighbourhood of $100----that is a nice new seat and some good rubber for your bike.

Why do you want to do this? What is wrong with your current setup?