When using the smbmount command line from a linux host to a windows share drive, the write permission is dropped. The username can write via normal windows sharing. The masks are set to 0777 on the smbmount. The mount works for read, but not write.
We don't maintain the smbfs kernel code. Suggest you test the cifs-fs
which is actively under development (http://linux-cifs.samba.org/)