I'm no lawyer (god forbid), but we just went through this discussion on my
BBS, so I now know a little about this, which is: There ain't no set rule,
and certainly no set number of lines or words. After much back-and-forth,
the best our resident lawyers could come up with was: You can quote little
pieces if you like, but don't print entire works (whether articles, poems,
or music).
So you, Magnus, and others who use quotes are likely in pretty good shape
-- though it certainly wouldn't hurt to give a citation somewhere in the
game (or the documentation) for where you got the quote from.
Neil