Love the site, saved my butt more than once with several iBooks and PowerBooks. Is there a list of Screw Guides that...

Sorry this is general, you can research specifics online. 2 issues are key: size/shape of the logic board, and arrangement of ports. PowerBook evolution ran in "families" (Mercury, Onyx,...) Within a family, boards were often interchangeable - I think the 400, 500, and 550GHz could be swapped out within the same screen size. Newer/faster processors, more features, redesigns meant later incompatibility. Also, the ports on the logic board need to match with openings in the case; if your board has all ports on the side but the case only has openings on the back, it will be difficult to plug in anything. Another example: I have a 17" PB 1.5 GHz with water-damaged logic board; my replacement options are limited to the 17" 1.33 GHz or 17" 1.5 GHz for fit and function (after 2 years of "casual" looking, I found an affordable 1.33 GHz with a cracked screen. Buying a new 1.5 GHz logic board would bust my budget, so I can handle a slightly slower processor.) Hope this helps.