In Windows 2000, XP the three key boot manager loading files are:
ntldr, Ntdetect.com, and boot.ini All 3
are in the root of active, system primary partition.
In Vista, Windows 7 the booting functionality (above 3 files if you like) have been replaced by:
bootmgr, BCD, and winload.exe Only bootmgr and BCD
stay in the root of the system partition. Winload.exe resides in windows/system32 folder of the boot partition. These can be separate partitions and by default MS/Windows places bootmgr and BCD in a separate 100MB partition (System reserved, active, primary). Winload.exe is in a separate Boot, OS partition. They can coexist in the one partition and many people appear passionate about making this happen (read the forum threads).
For Bios booting, the role of the MBR (Master Boot Record) on the first physical 512 bytes of booting device (typically HDD) remains the same.
Boot.ini can be edited with a text editor. BCD requires bcdedit.exe or via 3rd party programs like EasyBCD.
The move by MS in booting architecture has positives and some negatives (which can be overcome). It is thought to be consistent with a more widespread move to a UEFI (Unified Extensible Firmware Interface) architecture. The MBR is part of a 25 year old architecture and a change is probably overdue. Read some more here.