I believe TDP does not refer to power consumption, but to the heat generated in terms of watts.
Technically, you are right. But it makes a reasonable high end estimate of the power consumption. Intel docs say the the TDP is power dissipated if every i/o pin on the CPU is used. And because of losses in the motherboard power regulator, it will probably come pretty close.
I have an OC'd Q6600 (stock TDP 90 watts). Based on actual measurements, at stock speed and voltage, it pulls 8 amps (96 watts from the PSU.
leandrodafont, it takes suprising like computer power to move video from a hard drive to a video screen. I was going to build a dedicated HTPC, but I found that the little WD TV Live does everything I need. The little box eats about 10 watts when it is running. Figure anoth 10 - 15 watts for a USB drive.