I have an iBook 600 (14", if you think that matters), and I have a problem with my trackpad. I guess about 4 weeks ago, it started to give up on me for (short) periods. Sometimes leaving the iBook alone for a minute or two fixed the issue, sometimes it helped to restart. Anyway, as this became an issue, I bought an external mouse, so I can use the iBook, no problem. But, by now, the trackpad hardly ever, not to say never, works. Not the trackpad, not the button.
I think it's some physical problem (seeing how I can use the external mouse without a problem, and I fixed my disk and all the rest that can be fixed). Also, in the beginning, I noticed that the trackpad usually started when I moved the iBook in some way.
I see, reading some of the threads here, that many of you are technically quite versed, so I think, as I cannot count on any warranty (expired), I should try here before paying Apple way too much.