Or you can try doing it under the power settings, although I am not sure if that totally disables the SpeedStep action. It should be under Display settings, in the Screen Saver section, in the power section. Change it to Always On.
But I do know you can change it in BIOS, that's for sure.
My Q6600 is supposed to run at 2.4 GHz, but most of the time it sits at 1.6 GHz because of SpeedStep. I don't mind, it's smart to save some electricity and heating when all I do is type junk or watch a movie. It does jump back to 2.4 GHz whenever I do something more serious.
Don't disable SpeedStep, it's useful.
I wish the 8800GTX had something like that
Edit: I believe you've got a Q6700 (based on the default 2.67 GHz speed), but Vista was invented before the Q6700 so it has trouble identifying it and it leaves the model name empty. Are you getting updates for Vista from time to time? They should fix it, it's embarrassing.