Just to post a follow-up for people who were trying to connect to a standard install of WinServer 2003, and were unable to do so, due to error -5000. I was getting errors every time, regardless of the user settings.
The referenced hint above requires you to downgrade the security settings on the server. Instead, I changed one line in the file /etc/smb.conf/. Change the line that reads:
client ntlmv2 auth = no
to this:
client ntlmv2 auth = yes
After making this change, it works again. No need to restart or anything. This may not work for everyone, but it does solve the issue for me.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060518035327596