default_controller problem

[eluser]Santiag0[/eluser]
Hi! I'm starting with CI. I have a little problem when I try to set the router of the default_controller.

Code:

$route['default_controller'] = 'welcome'; //It's OK
$route['default_controller/([a-z0-9])'] = 'users/name/$1'; //Doesn't work :(

I need that because I need to copy the functionality of fotolog:
eg. fotolog.com/jhon
so i need a friendly URI, like myweb.com/user_loco
and the user see his profile.

Thanks a lot!!