Change FSB or External clock?

I've been reading my IT7 manual, and it says the FSB setting can be set to Low or High. That's it. What IS adjustable is the External Clock speed, which goes from 100MHz to 250MHz. All the guides I've read talk about adjusting the FSB speed, but that doesn't look possible. Am I actually supposed to adjust the Ext. Clock?

thanks

Sharkdiver gave me an awesome link that answered this question for me.

http://www.sudhian.com/faqs.cfm/fid/15/fcid/22.sud