Adding a Windows Server 2000 Network Share / Drive to a Windows 7 PC

In this case, it was also on a workgroup and will not accept the password because of the authenticated method that changed in W7.

You have to go into the registry to

HKLM\SYSTEM\CurrentControlSet\Control\Lsa

And then ADD a DWORD value of LmCompatibilityLevel and set it to 1 (one)

No reboots required, it should work immediately.