They dont need to have a fuse. You just need to have a good old US-UK converter and your set. I use my powerbook in the UK all the time and it runs on local voltage, so relax, your iBook is safe :-)
ps:: I normally use a multi with a fuse, when I have different things, like a monitor and external drive hooked up along with the powerbook. That way the fuse protects it, if there be an overload using all of them together