I installed both Windows 2003 and Win2K on my home PC's hard disk. I wanted to be able to dual boot both OSs, but I discovered that if you install Windows 2003 first on a separate partition, you aren't able to dual boot. You can boot only to Win2K.
Rather than uninstall and reinstall the OSs, I solved the problem by copying the Windows NT Loader (Ntldr) and Ntdetect.com files from the Windows 2003 CD-ROM to C:\. The latest version of these files can detect both OSs. Ntldr determines the location of the OS boot partition and launches Ntdetect.com. Ntdetect.com, in turn, obtains device and configuration information.