When you attempt to run Winnt32.exe from the CD-ROM of the CD-ROM for an x64 version of Windows Server 2003, or Windows XP Professional x64 Edition, on a computer that is running a 32-bit version of windows, you receive:

<CD_drive>:\AMD64\WINNT32.EXE is not a valid Win32 application.

To workaround this behavior, start your computer from the installation CD-ROM. This will cause the Setup program to automatically start.