Do yourself a favor. Find a gas company that sells the beer gas combination and ask if they require a N tank or will they use CO2 tanks. Don't buy anything until you get this answer.
http://www.northernbrewer.com/documentation/Hi-Res/nitro system.pdf
Using the Nitrogen Kegging System
Method A
This method assumes that you already have a separate
CO2 cylinder and regulator. The beer is carbonated to
a very low level with pure CO2, then dispensed at a
high pressure using beer gas.
1. Cold-condition the beer for several weeks to
maximize yeast flocculation; alternatively, use a
fining such as gelatin or isinglass. This will help
prevent the restrictor disc in the faucet from
becoming clogged.
2. Rack the beer to the keg and chill to facilitate
absorption of gas.
3. Force-carbonate the beer with CO2 only to
approximately 2 vols of CO2. Refer to the
following chart to find the correct regulator setting
based on the temperature of your beer.
3. Disconnect the CO2 and relieve any pressure in the
headspace of the keg.
4. Connect the nitrogen regulator/cylinder assembly
to the keg. Back the adjusting screw on the
regulator all the way out.
5. Connect the liquid line to the keg.
6. Open the valve on the cylinder to begin gas flow.
Using the adjusting screw, set dispensing pressure
to 25 psi; pour a sample and adjust dispensing
pressure as necessary.
Method B -Because the beer is not technically carbonated with
this method, you can save time and skip some of the
steps listed above. However, this method does require
additional components that are not included with this
system. If you use Method B to nitrogenize your beer,
you will first need to attach a stainless steel diffusion
stone to the gas-in dip tube of your keg (use about 2
feet of 1/4 ID tubing for a 5 gallon keg).
1. Cold-condition the beer for several weeks to
maximize yeast flocculation; alternatively, use a
fining such as gelatin or isinglass. This will help
prevent the restrictor disc in the faucet from
becoming clogged.
2. Keg the beer and chill to 35°F.
3. Connect the nitrogen regulator/cylinder assembly
to the keg, open the valve on the cylinder and set
the pressure to 15 psi. Allow keg to pressurize for
one hour.
4. Close the cylinder valve and relieve pressure in the
headspace of the keg.
5. Connect the liquid line to the keg.
6. Open the cylinder valve. Using the adjusting screw,
set dispensing pressure to 35 psi and pour a
sample; adjust pressure as necessary.