keys popped off, how can i put them back on?

It's 100% possible to fix a typical iBook keyboard...I put keyboards I've repaired on every iBook I sell. The trick is that when a key comes off, typically the "scissor mechanism" underneath, which is made of two pieces of plastic, comes apart as well. You will notice that one piece has two tiny knobs, one on either side, and these go into holes on the other piece. If one side or the other has come out, then trying to press the keycap down on the mechanism will not work, because the mechanism is not in the proper shape to accept the keycap. Getting the two plastic pieces together can be frustrating...I use fine-point tweezers, but you can also use the corner of a razor blade to pull one of the plastic pieces aside slightly so that the knob on the other fits in place again. Once the mechanism is in place, you can generally lift it slightly from the bottom and see the "scissor" effect work. If the pieces have completely come off and it's confusing as to which way they go, pop off another keycap and look at the mechanism in place on that key. Removing keycaps is like taking off a bandaid -- the quicker the better, and the slower you do it, the more damage.

If the pieces are damaged, you can replacements on eBay by typing "iBook keys", and you will find people who sell individual keys and scissor mechanisms for a couple dollars. But make sure the mechanism they sell matches yours, because there are several different styles.

If all else fails, you can buy a new keyboard, as they aren't too expensive, but it would be a shame to spend money if the fix is pretty simple.