iBooks have mini-VGA ports and come with mini-VGA to VGA adapters.
MacBooks and 12" PowerBooks have mini-DVI ports. The PowerBooks came with mini-DVI to DVI and mini-DVI to VGA adapters that work with the MacBook. (The MacBook doesn't come with adapters.)
15" and 17" PowerBooks and MacBook Pros have full-sized DVI ports and don't come with any adapters. They don't need any for DVI displays but do for VGA displays.