samba - Jun 2006 - Xp user opens file via Samba, but file is not locked after opening???

Hi.
I have Samba on my FC5 x86_64.
Problem:
When XP users edit the file, after a moment I open the same file with
Fedora, the file is not locked and also not read only! And I can write
on Fedora this file, however XP users are editing the file.


Is there solution for this, to lock the opened file?
So that other users can not write to it?


Thanks

-- 
Maris Dembovskis