Howto NFS shared writable space

[hobbes@easynet.be (Rémi Letot)]

Hi all,

I'm trying to setup a shared disk space with NFS. Till then, no
problem. But I want that people belonging to a specific group can
write to it, and modify every file in it. 

So I made the exported directory belong to the group, put the sticky
bit on it, so every file created in it belongs to the group. No
problem. But the permissions on newly created files are g+r, and I
need g+rw so that everyone belonging to the group can manipulate those
files without problem.

Is there a way to set this up? I have searched a lot, and can't find a
way. I can't believe that such a simple setup is not doable. 

Thanks,
-- 
Rémi