Generating a .img from tarball: The /dev/loop devices

I'm trying to make a .img from a tarball using the following script I found:

#!/bin/bash

# Packages required
# dosfstools parted 
# Can be run on any Linux system
# loop.max_part=15 must be in kernel cmdline (cmdline.txt for rpi)
# then reboot

echo "creating image to fit on 2Gb card"
dd if=/dev/zero of=arch-rpi.img bs=1M count=1850

echo "Partitioning"
fdisk arch-rpi.img <<EOF
o
n
p
1

+100M

t
c
n
p
2


w
EOF

sleep 5

losetup -f arch-rpi.img
sleep 5

echo "Formatting vfat"
mkfs.vfat /dev/loop0p1
sleep 5
mkdir boot
echo "Mounting boot"
mount /dev/loop0p1 boot
echo "Installing"

echo "Formatting ext4"
mkfs.ext4 /dev/loop0p2
sleep 5
mkdir root
echo "Mounting root"
mount /dev/loop0p2 root

wget http://ift.tt/1BKipqa
echo "Installing"
bsdtar -xpf ArchLinuxARM-rpi-latest.tar.gz -C root
sync
mv root/boot/* boot
sync
umount boot root
losetup -d /dev/loop0p1
losetup -d /dev/loop0p1
losetup -d /dev/loop0
echo "All complete, image arch-rpi.img created, compressing...."
zip -9 arch-rpi.img.zip arch-rpi.img

I'm doing this on my Raspberry Pi - Raspbian Wheezy. And when it gets to the line mkfs.vfat /dev/loop0p1 It says there's no such file / directory. I've read enough on Linux to know I'm trying to mount the .img as a loop device and then use mkfs to prepare the image for the tarball, but I don't quite know why loop0p# files are not there, they are listed by fdisk -l. What do I need to to in order to get this script I found working?