yes, but you will need a backplate from an 80GB model, because the 80GB drives are thicker than the 30GB drives, but other than that, the drive should work fine. But do make sure that the 80GB drive is from a 5th generation video, not a new iPod classic, this isn't a major problem, more of a precaution.
Here is the total list of what you must replace:
*60/80 gb rear panel
*60/80 gb headphone jack (it's about 1/4" longer
to reach around the thick hard drive)
*60/80 gb battery (longer to reach around HD)
*60/80 gb rubber bumpers (taller to protect logic board in thicker casing)