Restriction on creating files on shared folder on Vista from Linux

I have a small network of Vista and Linux machines. Each machine has a shared
folder, to which I want all the other machines to have unrestricted access.

- The Vista machines can access the other Vista shared folders correctly.

- The Vista machines can access the Linux shared folders correctly.

- The Linux machines can access the Linux shared folders correctly.

But...

- The Linux machines can access the Vista shared folders with read-access
and write-access (i.e. they can modify an existing file), but not with
create-access (i.e. they cannot create new files).

Does anyone know how to get the Linux machines to be granted create-access
to the Vista shared folders?

More information:

- Vista Home Premium
I have granted full control and access to "Everyone" and "Guest" on the
shared folders.

-Linux, Ubuntu Hardy 8.04.1. Using Samba 3.0.28a-1ubuntu4.4
I have granted full access to everyone on the shared folders.