Beer gas or nitrogen...or what?

I am looking to dispense beer in Nitro, Guinness style (although I will be starting with a cream ale). I have heard/read conflicting things about beer gas and nitrogen. I understand beer gas is used to push beer longer distances when co2 would require pressures that would over-carbonate.

Is beer gas what is used to dispense with a Guinness type tap or do I use pure nitrogen? How do I treat the beer as it comes off of aging. Do I carbonate, or do the same thing with beer gas or nitrogen, or what? I've got the faucet already (my birthday present) and need to buy a tank. What do I need? I have cream ale in secondary, about 3.5 weeks out.

Thanks in advance. I hope this isn't a re-occurring thread that just went away.

I have similar questions to yours and ran across this:
http://www.micromatic.com/draft-keg-beer-edu/dispensing-beer-blended-gases-cid-1793.html

Also found this:
http://www.northernbrewer.com/documentation/Hi-Res/nitro%20system.pdf


Cheers!

It's my understanding that you need a gas mix. CO2 will maintain the carbonation level in the beer by maintaining equilibrium, and the nitrogen is used so higher pressure can be used to force the beer through the restrictor disk in a stout tap.