I have a samba 3.0.2 server which I connect to from various windows 2000 and XP machines. Even if I set "disable netbios = yes", my Windows machines have to have netBIOS enabled to connect to the ...

Windows File sharing, SMB, is done over NetBIOS, you need it enabled to use it. You would disable NetBIOS for something like a WebServer that is internet facing and only needs to accept HTTP traffic ...