I spent a good hour trying to find something like this so I thought I should re post the link.
This uses a tool called ms-sys and all you need to do is boot into a linux live cd and install it (see link below) and then
ms-sys -m /dev/sda
Replace sda with the hard disk you want the boot record to be on.
and you are done
http://ms-sys.sourceforge.net/
Taken from
http://penguininside.blogspot.com/2009/06/fixing-windows-mbr-from-linux.html
