If you've upgraded your Mac to 10.4 and can no longer access a samba server, it's probably because of one or two configuration options on the samba server. 10.4 assumes passwords are encrypted. This is a good thing. It also seems to not work with SHARE level security. Switch Samba to USER or DOMAIN. Look in your smb.conf file for options like these:

encrypt passwords = yes
security = USER

Set them as above, create the smbpasswd file and set a password for your account, bounce samba, and try accessing it from the Mac again.