dd if=/dev/zero of=myharddisk.img bs=1000 count=0 seek=$[1000*1000*SIZE]
You need to make this file look like a block device (Choose a free /dev/loop device):
losetup /dev/loop0 myharddisk.img
partimage /dev/loop0 backupfile.000
losetup -d /dev/loop0
mount myharddisk.img /path/to/dir -o loop