If you have a local gas supplier that supplies "beer gas", then yes, it's fairly easy.
Beer gas is a blend of CO2 and Nitrogen that comes pre-blended in a tank. You could use your basic CO2 tank to fill, but you would have to buy the adaptor for a regulator. Nitrogen requires a higher PSI, so you'll need a regulator that can handle nitrogen. Check out micromatic.com for some good stuff.
If you don't have a supplier that has beer gas, you'll need to buy a seperate tank of CO2 and Nitrogen. You'll have to use a gas mixer to blend your gas before it hits your kegs. That can get fairly pricey.
I'm not sure if you can use 100% Nitrogen, but I'm sure someone will be able to comment on that.