PeToUSB

PeToUSB is a Win32 GUI application for formatting and making bootable, USB Flash Memory Drives and USB HardDisks and optionally copying the output from a successful BartPE/WinPE build to the device.

There are options to backup/restore the MBR on a device.
PeToUSB does not make the device DOS bootable, it makes it XP bootable (ie: the bootstrap code will look for NTLDR).
A lot of improvements have been made since version 2. Now it rewrites the MBR code just in case it's corrupted, this option can be disabled if desired; on removable media, the partition is completely rewritten. Also you are allowed to backup/restore MBR, view disk information, assign drive letters, and more.