I have installed multisite manager to my drupal 6.14 with on share hosting, so i have http://domain.com, http://domain.com/site1, http://domain.com/site2, i'm use single instalation, single database and my folder structures are

/sites
/sites/default/
/sites/default/settings.php
sites/all/
sites/all/modules
sites/all/themes

sites/site1.domain.com
sites/site1.domain.com/settings.php
sites/site1.domain.com/modules
sites/site1.domain.com/themes

sites/site2.domain.com
sites/site2.domain.com/settings.php
sites/site2.domain.com/modules
sites/site2.domain.com/themes

different settings.php for each sites are

  1. for my domain.com settings.php i'm use
    $db_prefix = array(
    'default' => '',
    'users' => 'shared_',
    'sessions' => 'shared_',
    'role' => 'shared_',
    'authmap' => 'shared_',
    );
  2. for my http://domain.com/site1 settings.php i'm use
    $db_prefix = array(
    'default' => 'site1_',
    'users' => 'shared_',
    'sessions' => 'shared_',
    'role' => 'shared_',
    'authmap' => 'shared_',
    );
  3. for my http://domain.com/site2 settings.php i'm use
    $db_prefix = array(
    'default' => 'site2_',
    'users' => 'shared_',
    'sessions' => 'shared_',
    'role' => 'shared_',
    'authmap' => 'shared_',
    );

I made a role content administration for each site so they can fully manage their content, and cannot see other site content on their contet list

My problem is