An attempted fix in  should be re-done.
According to http://msdn.microsoft.com/en-us/library/ms537503(VS.85).aspx we cannot distinguish between the two because the Windows XP Professional 64-bit had so much in common with Windows Server 2003 64-bit. In fact, the same service pack could be applied to either.
The original commit in , refs #1219 handle IE on Windows XP 64-bit (was detected as Windows Server 2003)
(In ) fixes #1219 - changed the OS string to reflect the ambiguity, i.e., 'Windows Server 2003 / XP x64'