Are you talking about pumping up at home, or when fixing a flat on the road?

If you're talking about regular pumping at home, get a floor pump -- no frame pump (and especially not CO2) will be as easy as a decent floor pump.

If you're asking about CO2 for road repairs, you need more than just a cartridge. Poke a hole in that and it'll launch itself into the woods (hopefully without smacking you in the face first). You'll need an inflator, which has a regulator that controls the flow of the CO2 coming from the cartridge -- not just on/off, but it restricts the speed of the flow to a manageable level.

I have one of these, mainly for its ridiculously small size and the fact that it can still be switched on & off:
http://www.nashbar.com/profile.cfm?c...3A%20Inflators

Its drawback is that it needs threaded CO2 cartridges, which means that I can't just go to Wal-Mart (or anywhere they sell paintball or pellet gun supplies) and buy a big box of unthreaded cartridges for six bucks. For that kind of convenience, this is the way to go:
http://www.nashbar.com/profile.cfm?c...3A%20Inflators

CO2 is no replacement for the free air of a frame pump, but honestly, it sure is nice when it inflates a tire so quickly.