samba-pdc ports ??

Hello, I've installed a samba-pdc server. I can't find my PDC fron a XP machine when samba and firewall are ON. If I turn my firewall off, so I can to see and to integrate my Windows machine on the domaine. After, if I need to use the resources, I can with my firewall ON. I don't understand this pount... So, somybody knows if I must open another specific diferent port than I have (137tcp, 137 udp, 139 tcp and 139 udp) when I put some machine on the domaine? Thank you very much and I'm sorry so much my english. Regards. frn