Cygwin dd under WinXP

normal: dd if=\\.\d: of=out.iso bs=4096

diskext

Extents for C:
Extent [1]:
Disk: 0
Offset: 57576960
Length: 20974464000
Extents for D:
Extent [1]:
Disk: 0
Offset: 21139001856
Length: 58860071424
Divide the offset by your block size 21139001856 / 512 = 41287113 and use that with skip=
dd if=\\?\Device\Harddisk0\Partition0 of=bootsector.bin skip=41287113 count=1