I would say the biggest is a 100GB, but a 60GB or 80GB should be a more affordable alternative. I've looked at trying to install an HD yourself in an iBook....and its pretty complicated. I think you'll probably have to take it somewhere, unless you've put computers together before, I really wouldn't try it. I'll try to find the website with the do-it yourself instructions so you can decide for yourself. I've replaced my RAM chip about four tiems in my iBook, but I wouldn't try a HD replacement.