For work I've got a HP 8510 p notebook and the fan noise it makes on idle is unbearable. It was annoying enough I was on a quest to find a solution. After many hours on the Internet I found the following site http://www.p35-forum.de/board/notebook-hardware-control/acpi-module/7332-acpi-modul-für-hp-8510p/ which talks about overriding the ACPI DSDT table.
After reading up a bit on the topic and learnt more than I ever wanted to about ACPI, I've managed to change the fan speed on my HP 8510 notebook. Now Vista SP1 x64 runs like my other notebook, quiet! Will have to see will it over heat or have any side effects.
I have no idea why HP releases notebook that are so noisy out of the factory. Their engineering department should be reeducated that noise should be minimal on the desktop in the office.