The FIXMBR XP is a Windows XP recovery console command for fixing the MBR file. The MBR file is the first sector, 512 bytes, on the hard drive and is therefore subject to virus infection and other problems. The MBR contains hard drive partition information, boot record pointer information, and information for boot strapping the operating system. The Fdisk DOS utility will do the same thing in the DOS that FIXMBR does in Windows Recovery Console.
The Windows Recovery Console can be started by booting the computer using the Windows install CD to run FIXMBR XP. If your computer didn’t come with a Windows install CD. You can make one using nLite and the i386 folder on your computer. nLite is a great free utility that can be used for creating custom Windows install CDs that are fully automated and setup to include all drivers, service packs, security patches, and other important tweaks and files you might need. You can also use nLite remove keyboards, languages, and other files to lighten the size of the Windows install disk and provide a faster install.
The following is a YouTube video on FIXMBR XP that you might find useful.

FIXMBR
The FIXMBR website has some additional articles you might find useful.
The Recovery Console can be used to boot your computer and recover files and fix several computer related problems. There are many commands that can be accessed in Recovery Console, including the ability to start or stop services, some admin tasks, format hard drives, and read and edit NTFS file system files.
You can start Recovery Console by rebooting your computer to the Windows setup install CD. You will need to set your BIOS so that the computer will first boot from the CDROM.
Once started you will need to select the operating system and use your administrator password to logon.
Once logged on you can use the help command to view all the different commands available. Some of these commands are del (delete file), copy (copy file), md (make directory, rd (remove directory), attrib (change the attributes of a file), chkdsk (checks hard disk and provide a report), dir (displays files in a directory), and exit (exits the Recovery Console and restarts your computer)
The command FIXMBR can be used to correct or repair the MBR (master boot record) file. The MBR file is in the first sector of the hard drive and contains partition information needed for the operating system to boot and recognize the different partitions and logical drives available.
The Recovery Console can be very useful for repairing files and recovering or correcting a non functioning operating system or faulty hard drive.
FIXMBR
The FIXMBR website has some additional articles you might find useful.