[kh99]

If you add columns to the user table, they will load with the rest of the userdata and you won't have to do anything. If you use a separate table with a userid column, then you can use a plugin at hook location fetch_userinfo_query and set the variables $hook_query_fields and $hook_query_joins to add your table to the query. For example:

$hook_query_fields .= ', mytable.*';
$hook_query_joins .= ' LEFT JOIN mytable ON (mytable.userid = user.userid) ';

See includes/functions.php, function fetch_userinfo().

Edit: I just reread what you posted - if you don't want to read your info directly from the database, you could instead use a plugin on hook fetch_userinfo to do whatever you have to to find the data for user $userid, then add your info to the $user array.