Take a look at the top of your logic board by carefully undoing the display cable from the logic board Link text. You do not have to remove the entire display or remove the front panel to see the model number under the cable.

If it says, "820-1763-A", this means that this logic board is the first generation iPod video... and meant only for the 30/60GB hard drive models, and it will not support an 80GB.

If it says, "820-1975-A", this means that this logic board is the second generation iPod video (5.5)... and can work with the 30, 60 and 80GB iPod video hard drive (maybe even high size hard drives, but I have never tried this theory). Besides it being able to use an 80GB hard drive, it has the Search feature/option on this board.

I do not know why iFixit doesn't state this fact. But I made the discovery after repairing many iPod videos and had the same problem.