. Если про Joomla 1.5 говорите.
Synchronize Users CB joomla component
For Joomla 1.0.x and 1.5.x (native).
Synchronize your users with this joomla extension no matter where your joomla sites are located!
CB 1.1 & CB1.2 support.
Using Synchronize Users CB joomla component you can have registered users and upcoming new registered users synchronized from one Joomla site to all other listed Joomla sites no matter where the sites are located. You are also able to choose what usergroup a user will be synchronized to on the subsite.
The component works the following way:
You install the component on the main site where a user makes a new account or you already have existing users. In the component you list which other sites users should be registered on (you configure the settings of the subsites including the link of the subsite where users will be redirected on autologin). After you have synchronized the users manually once, you don't need to do this again. New users are handled automatically even if they change their user info.
PLEASE PAY ATTENTION:
To use the autologin option, you'll also need to install the component on the subsites. When the component is being installed, it automatically installes the mambot and cb plugin. You'll just need the component and published mambot, so you should unpublish/delete cb plugin on the subsites.