hey, how can i let the user remain logged when they switch between slave site?

With the core Jms multisite, you can do that for the slave site that are in subdomain or subdirectories.
(ie. subdomain.domain.com and domain.com/subdirectory)

In joomla 2.5, remain logged on subdomains require that you setup the "global configuration" with the "cookie domain".
In Joomla 1.5, the "cookie domain" is automatically added by JMS as that didn't exists in joomla 1.5.


In the case where you want to remain logged with different domain, you need the "Single Sign-In for domains".
www.jms2win.com/en/joomla-multisite?page...51&category_id=1

See also the demo
slave1.mywebsite2win.org/

if my domain is playerzone.eu and joomla is in the root how i have to set the cookie? and for the subdomain (firefall.playerzone.eu)?

.playerzone.eu

dot followed by the domain name.
This mean "wildcard" followed by the domain.

thanks, have i to set .playerzone.eu in every slave site? and i leave empty the cookie path? thanks again

( now i have set .playerzone.eu in master and slave site but single log ing don't work )

Check if you have an apache suhosin module installed.
When it is installed, this suhosin module perform addition session check and forbid to share the session between the website.

When you are logged in a website, use the joomla "php information" to verify that the "cookie domain" is correctly setup.

The domain that you setup declare on which domain the session can be shared. Other domain will be excluded.