Hello, just brought a new computer 2 month ago with Althon TB 800 and the Motherboard is a K7T pro 2. I also got a geforece 2 Mx card and a Sound Blaster Live on my board, I try the bios but I don't think there is an option for overclocking. I have got a large fan and heat sank. I want to overclock it to around 850 - 900
Well, first you need to make sure that the motherboard will allow you to adjust FSB settings and multiplier settings. If it does all you have to do is take the processor out, go find a mechanical pencil with "HB" lead, then close the L1 bridges. If you look at the processor, there are little tiny gold dots all over it and they're all in lines. Look for the dot set that has "L1" next to them. Then, scratch lines over the dots to close the bridges. Next, throw the CPU back in the board and overclock! I suggest you read tom's guide on overclocking the Thunderbird- it's more comprehensive. Also, make sure that is a good heatsink. Just cause it's big doesn't mean it's good.
PS, There are probably jumpers on the motherboard that will allow you to overclock (multiplier and FSB settings)
As mpjesse pointed out make sure you buy a good heatsink. The generic one you most likely got with your board will not work and your CPU might fry. There was a recent article still on the main page about 17 different heatsinks. Start reading and be CAREFUL.