This new Setup program behavior permits later versions of the Ntldr and Ntdectect.com files to remain on the computer and not be overwritten with  an earlier version of these files. For example, when you perform an installation of an operating system that includes later versions of the Ntldr and Ntdetect.com files, Setup  replaces those files on the hard disk. However, if the versions of the Ntldr and Ntdetect.com files of the operating system that is being installed are earlier  than the versions that currently are on the hard disk, the files on the hard disk  are not overwritten by the Setup program.
Note This change does not affect the installation behavior of operating systems that are earlier than the operating  systems  that are described in this article. Windows installations  that are earlier than  either Windows x64-based editions or Windows Server 2003 SP1 slipstreamed  still overwrite the Ntldr file and the Ntdetect.com file without checking the  file versions. 
The Ntldr and Ntdetect.com files should always be the most current version of the operating systems that are installed. The most current version is always backward compatible with prior versions.
Technical support for Windows x64 editions
 Your hardware manufacturer provides technical support and assistance for Microsoft Windows x64 editions. Your hardware manufacturer provides support because a Windows x64 edition was included with your hardware. Your hardware manufacturer might have customized the Windows x64 edition installation with unique components. Unique components might include specific device drivers or might include optional settings to maximize the performance of the hardware. Microsoft will provide reasonable-effort assistance if you need technical help with your Windows x64 edition. However, you might have to contact your manufacturer directly. Your manufacturer is best qualified to support the software that your manufacturer installed on the hardware.
For product information about Microsoft Windows XP Professional x64 Edition, visit the following Microsoft Web site:
 For product information about Microsoft Windows Server 2003 x64 editions, visit the following Microsoft Web site: