The FIXMBR command no longer uses DOS and the fdisk utility is no longer available in Windows XP. However, there is this new FIXMBR command function that can be used in the Recovery Console where you can also find other important maintenance tools. You can start the Recovery Console from an original Windows XP install CD or you can also install it to the hard drive so that you can access it during startup. To install it to the hard drive type the following at the command prompt: X:\i386\winnt32.exe /cmdcons (X is the letter of the CDROM drive where the Windows XP install disk is.) When you startup the Recovery Console you will need the administrator’s password access the drive.
There are several familiar DOS commands that can be listed by typing HELP at the prompt, such as, attrib, del, more, delete, mkdir, dir, format, cd, help, chdir, rd, chkdsk, cls, exit, rename, copy, md, and rmdir. These commands can be used to repair and modify all files and folders on your hard drive. The Windows XP FIXMBR command and Recovery Console has proven to be a very helpful maintenance tool.
I also have a YouTube video on FIXMBR that you might want to checkout.
Fdisk MBR
The Fdisk MBR website has some additional articles you might find useful.

[...] the same thing in DOS. There is a site an article explaining FIXMRB in more detail at: FIXMBR Command September 25th, 2009 | Category: Computer [...]
Hello. I have an nlited XP install on my Eee Pc. I think I have an MBR problem, but upon booting from my original Nlited cd, I am only given options to delete partitions and reinstall windows. Repair console doesn’t even show up. do i need my original install cd (the non nlited version)?
Hello Logan, Booting with the nLite disk you should be able to select R to enter the Recovery Console. The message is:
When the “Welcome to Setup” screen appears, press R to start the Recovery Console. If the option is not there then the nLite version you have might have removed the Recovery Console utility and you will need the original install CD.
Hope this helps.
Regards, Greg