How are we generating SID's when a request from NT comes.

[Karthikeyan]

Hi ,
       When from the NT box if I click on a file in my samba home
directory and click its property and then
permission .  Now I am able to see all my SMB users here .
       When I  add a particular user and give him a access right .it
should lead to NT_TRANSACT_QUERY_SECURITY_DESC  and
NT_TRANSACT_SET_SECURITY_DESC call
for this we from samba side has to give some SID to the NT box .
actually how are we generating these SID ?
where these SID are stored. ( I am using samba 2.0.7)
please clarify this issue for me.
with regards
karthik