http://pda.hardware.info/en-US/articles/amdnY2pvZGOa/Research_actual_power_usage_modern_PCs/
http://www.pcsforeveryone.com/product_info.php?products_id=27448&cPath=1749 - says the Celeron 331 uses 84 watts. That's a lot of power. Must be the max rating.
Old chips don't use too much energy... but they are way too slow. The processing power per watt is much too low.
http://www.hardwaresecrets.com/article/187/4 - great article on chip power consumption.