Mac cant access sharing in windows 2008 domain

We have windows 2008 as domain controller for our student lab. Mac version 10.6 Leopard can access the windows 2008 DC sharing folders without a problem. However Panther and Tiger cant access the same sharing folders. If we try smb://windowsipaddress, the logon screen display, but we will receive "Could not connect to the server because the name or password is not correct" message if we type the dolman username and password to logon.

We have tried the following suggestions we found in the Internet.

1. Network access: Sharing and Security Model for Local Accounts: Classic - local users authenticate as themselves.
2. Disable: Microsoft network server: Digitally sign communications (always)
3. Disable: Microsoft network client: Digitally sign communications (always).
4. Modify NTLM settings.

For a test, we also installed one windows 2008 server to out windows 2003 domain. Both Panther and Tiger can access the windows 2008 sharing without any problems. Could the problem is that the server windows 2008 DC? Any suggestions?