Abit BH-6 MB with 566 Celeron. Ran at 850 the first time I fired it up, good ever since. I have an extra case fan, and a large CPU fan on the chip, no other extraordinary measures. You may need to upgrade your MB bios as well to allow all the multipliers and FSB settings to match up.
Can't remember the voltage I'm running right offhand, but it was what was in the article I read (Anandtech.com I think). If you want a link to a "how-to" go over to AGW and search their hardware forum. There's a couple of topics in there (Hobo was the originator) with a link to a good article on it.
[This message has been edited by jedi (edited 08-10-2000).]