I took apart a 5th Gen iPod with Video 80Gb to replace a cracked screen. Wasn't too had just make sure you get one of those plastic prying things to get the metal back off. Don't use a screw driver because you'll end up chewing up the plastic fascia pretty bad and it might not fit back on.
For reference, you get 20hrs playback if you don't change the song because the hdd spins up only once to load the song into the flash buffer. I only ever got about 9-10 hours of real use out of it.