samba - Jan 2005 - Directory readonly with rw permission for files

Hi folks,

I'm migrating a customer old NT server to a Samba/Mandrake server. 
Everything is working fine and fast.

The only problem I found is that some directory structures must be 
readonly but the files inside this directories must be read-write to the 
group.

Only the administrator can create/delete directories and he did it manually.

Is it possible to do that with Samba without using ACL ?

Thanks in advance for any tip.
Josir Gomes
Rio de Janeiro - Brasil