samba - Aug 2000 - sharing files to particular user in one group

Hi,

among 3 users say A,B and C  I need to give access of Read Only to B and
C and RW to A..how do I do that ???

Comment = abc group
path = /home/abcgroup
write list = @staff  ( what do I write here group name or user name) ?
read only = ?

Please help..thanks in advance..

Kishu