Yep I'd like to know this too I know with my Hitachi drive there was a disc utility to turn things like this on and off, maybe it's the same for Western Digital drives?
I just ordered the 150Gb Raptor. It looks ideal for what I do. My T7K250 gets thrashed a lot when I try and do one very disk intensive activity and one other that may or may not be...even just switching to a browser can take ages if the drive is being thrashed. This should speed things up nicely and the size is perfect, 74Gb wasn't enough for me.
On pre-order at overclockers.co.uk.