Try replacing:

dd if=/dev/sda1 of=/dev/sda5/xp0.dat
with

Code:
dd if=/dev/sda1 of=/mnt/sda5/xp0.dat
or wherever mount shows /dev/sda5 is mounted (might be /media)
see also

http://wiki.linuxquestions.org/wiki/Dd#Create_a_backup

HTH