I found this on making a Emergency Repair Disk: Repair Disk
Steps Performed by the Emergency Repair Disk
The following steps are performed by the Emergency Repair Disk:
Runs CHKDSK on the partition containing Windows NT system files. On Intel x86 machines, also runs CHKDSK on the system partition (this is optional and must be enabled manually).
Verifies that each file in the installation is good, through a checksum algorithm. If files are missing or corrupt they are restored from the installation disks.
Replaces the default system and security (SAM) Registry hives, subject to user confirmation.
Reinstalls Boot Loader (that is, the boot sector, BOOT.INI, NTLDR, etc.)
Steps Performed by the Emergency Repair Disk
The following steps are performed by the Emergency Repair Disk:
Runs CHKDSK on the partition containing Windows NT system files. On Intel x86 machines, also runs CHKDSK on the system partition (this is optional and must be enabled manually).
Verifies that each file in the installation is good, through a checksum algorithm. If files are missing or corrupt they are restored from the installation disks.
Replaces the default system and security (SAM) Registry hives, subject to user confirmation.
Reinstalls Boot Loader (that is, the boot sector, BOOT.INI, NTLDR, etc.)
