They'll almost undoubtedly still be running with G4's, possibly a bit faster. The eMac might have better drive/GPU options, and the iBook might have improvements to CPU speed and/or screen res and/or disk speed and/or GPU. Of course, that's all quite vague.
Basically, no one here has any good idea what Apple will have in the six months or so it'll take to release Tiger. I'm sure the systems will run Tiger just fine, but, beyond that, no one knows.