“author” default permalinks

due to modrewrite messing up our other directories’ access, we have had to use “default permalinks”… however, i cannot figure out how to make a post’s “Posted By: [author]” link to the post’s author page… it just 404’s…. what would i do to access “user ID 2’s” page? would it be index.php?u=2 or what? so far all i can see from searching around is the index.php?p=# for a Post’s URL but nothing for an Author’s URL…