it's all here: http://blog.koloda.pl/wordpress-panel-logowania.html
in case you don't know Polish, here is what you have to do:
open wp-login.php and find the line with "case 'login' :" below that you have a code executed when someone tries to log in. You have to look for something like:
if ( !isset( $_REQUEST['redirect_to'] ) )
$redirect_to = 'wp-admin/';
else
$redirect_to = $_REQUEST['redirect_to'];
and change it to:
if ( !isset( $_REQUEST['redirect_to'] ) || empty( $_REQUEST['redirect_to'] ) )
$redirect_to = get_settings('siteurl').'/';
else
$redirect_to = rawurldecode( $_REQUEST['redirect_to'] );
Check if users who have permission to add/edit posts are also redirected to proper side. If not you have to comment the line:
/* if ( !$user->has_cap('edit_posts') && ( empty( $redirect_to ) || $redirect_to == 'wp-admin/' ) )
$redirect_to = get_option('siteurl') . '/wp-admin/profile.php'; */
It may be a bit differed in wordress 2.6, but I guess you will have to use your brain and find similarities.