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