Time to upgrade

I've been thinking about upgrading the OS on my iBook for oh, about 2 years now but will finally get around to it this weekend I hope. The big reason for not doing it before was the fact that I'd have to reformat the drive and I live in fear of erasing useful data or not being able to open it from the back up. Anyway, I've found this very handy site and am planning on losing all my passwords and data upgrading this weekend. Alternatively I could go down the traditional route and buy a new iBook with 10.4 already installed on it.