I found this over in the Tiger discussion area at Apple's website, and thought I would share it. If you are having trouble mapping network mount points from a server using an older version of Samba (a.k.a. SMB or Windows sharing), here's a workaround...
Tiger now assumes that your SMB server accepts encrypted passwords. Older Windows NT and Unix/Linux servers running Samba (versions older that 3.0) are configured to accept plain text passwords. It is highly recommended that the severs be reconfigured to accept encrypted passwords. However, below is a fix to tell Tiger to send a plain text password for authentication. This assumes you have a working knowledge of the Unix command line:
[default]
minauth=none
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050506120948120