where MySQL data lives
On my mac, MySQL data is stored in /usr/local/mysql/data/tablename (I always want to know where things are so I can go and "ls" them. That's my [small, plastic] hammer.) For MyISAM tables, there are three files (approximately. Messing with table/db data from outside MySQL is asking for trouble.): tablename.MYI, tablename.MYD, and tablename.frm. As far as I can tell, *.MYI are indexes, *.MYD are data, and *.frm are table definitions (that one's a guess). more on .MYI files.
p.s. the mystery 700mb: the table data files themselves are appropriately sized (2mb + 31mb = 33mb total, same as I calculated they should be) and the indexes aren't insane (4mb + 41mb = 45mb total). so I still don't know what's up.