One would also need to rebuild samba from the source as supplied from samba.org to add back the missing older smbfs and related samba support.
Realise that the cifs filesystem is what is supported by the kernel. I think you will need to read the Samba 3.0.23 release notes to understand what the differences might be causing the problem. The Samba 3 Reference and How To guide also goes through the changes between the different versions of Samba. The biggest change may be due to the better domain controller support and the depreciation of the "security =
I think that upgrading the server or at least the samba package if possible would be a good idea. You may run into problems with changes make by MS Vista when it is accepted in your network. However, most of the problems would be on your host, accessing someone elses share than on the server. There may have been subtle changes in the authentication protocol that vista uses. MS used some shortcuts in the past and they tightened up on them. You may have the Samba3-HOWTO reference as either part of the samba package or a samba-doc package. Part IV deals with Upgrading and Migration. Also read the WHATSNEW.txt file that came with your Samba3 installation. There is a cifs.txt file in the kernel source Documentation.