Enable PHPSSID cookie and others to www.host or host

Hi,

I have very big problem, i'm trying to solve it from feew hours and i'm still get nothing.

I create server, put my website, and start codding...

After feew month i have website, and problem...

Cookies is valid only when i use -> hostname.com
when i use www.hostname.com is invalid... :/

I know about option in php configuration

session.cookie_domain =
What should i put there...

When i put hostname.com -> valid for hostname.com
WhenI put www.hostname.com -> valid for www hostname, for hotname invalid...

Agchhh

I cant find any information about ANY ! WILDCARD...

You know, normally we using wildcards like %

Is there any idea to put there something like this
%hostname.com ?

Or any other idea... use modrewrite to put ALL request from www to http

Please help me, i'cant work without it...

regards