truc bizarre vista -> ubuntu ( samba )

salut a tous
Alors j'ai un petit probleme bizarre
je possede un reseau XP ( x2 ), vista et ubuntu gere par samba pour la gestion linux/win
voici mon smb.conf

[global]

	workgroup = MSHOME

	server string = Server (Samba, Ubuntu) %v

	security = user

	map to guest = bad user

	guest account = nobody

	printcap name = cups

	disable spools = yes

	show add printer wizard = no

	printing = cups

	hosts allow = 127.0.0.1 192.168.0.0/7

	hosts deny = all

	wins support = no

[printers]

	comment = All Printers

	path = /var/spool/samba

	guest ok = yes

	printable = Yes

	use client driver = yes

	browseable = yes

[Partage]

	comment = Partage

	path = /home/franck/Partage

	read only = no

	available = yes

	browsable = yes

	public = yes

	writable = yes

	guest ok = yes

[Server_ubuntu_80GO]

	comment = Server_80GO

	path = /media/disk-1/Server_ubuntu_80GO

	read only = no

	available = yes

	browsable = yes

	public = no

	writable = yes

	valid users = serveruser

Le probleme est que sur le poste vista j'ai besoin de me logguer des que j'accede au pc ubuntu alors que xp me demande un login uniquement pour l'acces au partage serveur, ce qui est normal vu mon smb.conf ( enfin je pense   )

si vous avez une petite idée