Actually, downloading and archiving is pretty easy. It's transferring over to any other format that is difficult.
Find a program called "PG Offline" (version 4) from a company called Personal Group Ware.
It's an easy to use archiving tool with a 30 day free trial and no bugs as far as I can tell.
You log into your Yahoo Account ~through~ this program and can then download all the messages (almost 26,000), pictures and files to your local computer. Once you've captured the messages the program provides a pretty nice interface for reading and searching them. You can archive to a database, but I've not been successful at getting any other database software to make sense of it because a) it's proprietary software and b)Yahoo is a proprietary format.
I did copy-paste operations until MS Word cried "uncle" and have been slowly wading through 9 million plus words from the group, fully 1/4 of them advertising and spurious HTML code.
At any rate, if you choose to purchase ($40 or $50) that PG Offline program you'd have a great tool to keep the entire Yahoo group archived and available off line. I'm not affiliated in any with that software other than a customer.
SM 209, Adagio
USVI, Passport Pending :)