Windows 2003 File Sharing

I have my Macintosh Clients authenitcating via Active Directory on a Windows 2003 Server. The authentication works fine but when I go into connect to server, then type in smb://(name of the Windows 2003 server) it gives me the error:

"Could not connect to the server because the name or password is not correct"

However, when I use connect to server and type in smb://(name of a windows 2000 server) I can access the shares immediately and it does not ask me a username or password. I disabled "Microsoft Network Client: Digitally sign communications (always)" on the Windows 2003 Server. People on the Windows side have no trouble authenticating to smb shares on the 2003 server, but when they go to the Mac they cannot authenticate. I went through terminal to see if I could connect to the shares via smbclient and was able to.

I tried smb://(a username)a valid password)@(2003 server name) , both the login name and password are shorter than 8 characters, but I still get the "Could not connect to the server because the name or password is not correct" error.