First of all install dislocker, for doing that install aptitude and then

$sudo aptitude search dislocker

once you find dislocker install it, with:

$sudo apt-get install dislocker

once you have it installed, then you should run something similar to this:

$sudo fdisk -l

to discover your disk, and then

$sudo dislocker -u[YOUR_PASSWORD_GOES_HERE] /dev/sdb1 /mnt/hdext
$sudo mount /mnt/hdext/dislocker-file /mnt/hd