[Samba] file locking/sharing

[sam wun]

Hi,

I m using Samba 3.0.4. The problem is the if user1 created his file in 
the Public directory, the new file has the user name of user1 with 
permission 770 on the new file.
User2 can read and write to the file as well, but it doesn't change the 
ownership of the new file. After the new file has been modified by 
user2, the new file's ownership still displayed as user1.
The second problem is while user1 reading the file and user2 also want 
to the same file, but user2 does not receive warning that the file is 
being by another user, and much worst, user2 now can write to the file 
and save the file regardless user1 still reading the same file.

Is there any way I can define file locking regarding to file sharing in 
the public directory in Samba?

Thanks
Sam