(I am making this a new answer rather than a comment, because I am adding information relevant to the question.)
In addition to the logic board situation, you would need the following parts to upgrade to a thicker hard drive such as the 80 GB:
* 60/80 gb rear panel (thicker to accommodate a thicker drive)
* 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)
(good addition to the discussion, Majesty!!! It's important to bring up the other components that need to be changed.)
Rsharich/bac: as for the logic board situation, this is the first time I have found clear, quantifiable information about the significance of the logic board. While I was aware of the difference in model numbers and search function, I have had zero trouble using the boards interchangeably between 30 and 60 GB models. The 80 GB issue, however, is quite compelling!
Here's the good news: iFixit sells only 820-1975-A boards (which work in both revisions), so there isn't a compatibility issue with our parts.
Here's the bad news: we only have 820-1975-A boards, so I can't verify the information about the 820-1763-A boards!!! I will certainly do so as soon as I have access to said board.
Regardless, this is EXACTLY why we have the Answers forum!!! We cannot possibly know everything about all these machines, and drawing upon the expertise of others is so valuable for us and for customers. Thanks for the insight (+1 each is the least I can do!)