I believe I have two fans total. One fan for the processor and one 80mm case fan. And that heatsink is that big because the processor class was nearing its end (in a similar fashion that Intel upgrades its P4 line with newer chips under the same name, Apple does this with its G4 chip) in clocking headroom. It only reached +67MHz before the proc was changed to DDR-SDRAM and the multiplier was lowered to accomodate the higher bus speed.
The Geforce 4 Ti has a damn loud fan. Without it inside (with a passive heat geforce 4 mx) the system is much quieter.
I think I would know the model of my own computer, but if you want proof here you are. A screen grab of this thread being written, my OSX system info and my OSX system profiler window.