Yeah, and plus, the stock heat sinks on the X2 models, have copper heatpipes, which the stock heatsinks that standard Athlon 64 models don't. So you'll find you may not need to buy an extra heatsink/fan.
Heatsinks work alot better when they are made from copper, and/or have copper heatpipes.
They have a special formulation of liquid in the pipes that when heated, rise, taking heat with them. When they reach the top, the heat is taken away, and the gas cools, turning it back into liquid. The process is repeated over and over.
This type of system is how water cooling works, and with heatpipes, the same type of performance (compared to a cheap water cooling system), can be achieved, and quieter than standard heatsinks too, since the fan doesn't have to work as hard, to get the same result.
So, I'd say to try with the stock first. If its not up to your tastes, switch
I think so yeah. Are you talking about case cooling?
On mine, at the moment (just upgraded heatsink/fan), I have 1 80mm fan blowing in cold air. The heatsinks then taking that and turning it into hot air, which is then being exausted through a front 120mm fan.