samba - Oct 2004 - Permissions

hello,
I created a share "test"
I would that mydomain+gp1 write in this folder and mydomain+gp2 read only in
this folder.
I don't know to do that.

Could you help me please ??

arnaud

Debian 3.1 / Samba 3.0.7 / winbind 3.0.7