BuddyPress.org

It’s not going to be that easy, after all IE doesnt work that well with something fixated at the bottom of the screen.

Try this, it’s a jQuery plugin.

http://www.neeraj.name/blog/articles/870-always_at_bottom-jquery-plugin-which-keeps-footer-at-the-bottom-of-page

Only instead of a footer, put your buddybar at the bottom.