On backing up the MBR.

[lugoteehalt]

Windows 98 would not boot on dual boot system due to fiddling about with msdos fdisk.

Restored the master boot record, MBR, and it worked.

This from memory:
Backup MBR with:
dd if=/dev/hda of=MBR-backup bs=512 count=1

Restore the MBR by simply swopping the if and of bits.

[saikee]

It is a lot safer to use a Dos floppy or a XP/Win2k installation CD and get it from the horse's mouth.

Task B1 and B2 of my last link refer.

Apart from Vista the Dos and Windows up to Xp share a common MBR. Also the MBR from Freedos, in CD or floppy, will do the same trick. Why make thing hard when there are so many easier ways out?

I recommend the MBR to be generated because that is what every OS is supposed able to do, and I haven't met one that can't deliver it. Once the step is known a user has no fear of losing the MBR.

Having said the above there is nothing wrong using Linux's dd, as proposed by OP, to achieve the same thing.