Download DiskExt.zip and unzip it. Copy \Release\DISKEXT.EXE to a folder in your path.

When you open a CMD.EXE window and type diskext /?, you receive:

Disk Extent Dumper v1.0
Copyright (C) 2001 Mark Russinovich
Sysinternals - www.sysinternals.com

diskext \[drive1 \[drive2\] ...\]
    Drive1 and drive2 are drive letters.
    Ommiting drives dumps extents for all drives.
When I typed diskext on a lab computer, I received:
Disk Extent Dumper v1.0
Copyright (C) 2001 Mark Russinovich
Sysinternals - www.sysinternals.com

Extents for C:
   Extent \[1\]:
       Disk:   0
       Offset: 41126400
       Length: 24116520960
Extents for D:
   Extent \[1\]:
       Disk:   0
       Offset: 24157647360
       Length: 48636080640