You can do it with an iBook. You have to apply a patch of some kind. I think its the same one which allows you to run dual displays properly.

A link to a program that will do this for you was posted on this thread:

http://www.macmod.com/component/option,com_simpleboard/Itemid,/func,view/catid,46/id,10010/#10010

Here is the link again:

http://www.rutemoeller.com/mp/ibook/ibook_e.html