It's been a while since i've set up a samba server, but I'm taking my LAMP off my workstation and set up on a dedicated server. Most of the configuration of smb.conf was straightforward. The Vista box took a while to discover the server (slow to do anything!) but finally showed 'server' on the network although It stuck with not being able to log in.
So I tried from the server with 'smbclient -L server -N' and got the error message NT_STATUS_LOGON_FAILURE
By adding a smbuser 'smbpasswd -a [username]' this error is fixed and I can see the samba shares fine. I remembered to add a samba password for the user and there was no complaint that the user did not exist in smbusers. So if you're getting this same error message try this, it was not obvious to do this but there you go.
Hope this helps.