Ntldr contains the NT boot code

Ntldr contains the boot code for Windows NT-based programs (Windows NT, 2000, and XP). It's running from the time the master boot record (MBR) hands control of booting the computer to the Windows operating system until the Windows 2000 kernel is initialized. In systems configured for dual (or more) bootup, Ntldr offers a menu of operating systems to load (based on the values in the file Boot.ini). This menu appears on what's known as the bootstrap loader screen. If you select a different operating system than Windows 2000, Ntldr's work is finished. It passes control to Bootstrap.dos (the file that contains the boot sector for the other programs). However, when you select Windows 2000, Ntldr runs Ntdetect.com to detect hardware. You can tell Ntdetect.com is running when the message "Starting Windows…" is displayed, along with a progress bar at the bottom of the screen. If all goes well, Ntldr initializes Ntoskrnl (the Windows 2000 operating system kernel), which it loaded into memory earlier in the process. When the Windows Log On screen appears, you're almost home free, although a startup isn't considered a success until you log on. For more information about the Windows 2000 startup process, read Microsoft's online article from the Windows 2000 Server Resource Kit.