The latest MAC OS X can talk direct SMB to pick up files from Windows Shares. However default security settings in Windows render the MAC unable to authenticate properly, even though it can see the shares.

You need to disable the Digital Signing of Communications for the MAC to be able to talk to a Windows 2003 Share.

Credit  must go to Drew Mcellan for the resolution of this problem. See the full article here.
 

In Short....

Go to Administrative Tools, Domain Controller Security Settings, Local Policies and Security Options.

Set "Microsoft network server: Digitally sign communications (always)" to disabled.

Then at a command prompt type in "gpupdate".

Browse and authenticate via the MAC.