Yeah, Ca.net has some good information. Not too many people here know too much about classics and external air set ups. And I agree, the pricier set up is more versatile; I was just listing the CO2 power booster as a cheaper alternative. And Bauer CTU, where do you live. What is the climate/temperatures like? If you live up North, HPA is probably the way to go. But if you live down South, I would just go with CO2 because it is cheaper to get started.
EDIT: emu, how big is your HPA tank? $150 for a whole HPA set up is a great deal.