Converting

Raw to qcow2 (from http://lnx.cx/docs/vdg-2/html/ch02s04.html)
qemu-img convert -O qcow2 original-image.raw image-converted.qcow
Qcow2 to raw (same place)
qemu-img convert -O raw image-converted.qcow image-converted-from-qcow2.raw

Mounting via loopback

Mount raw (from http://alexeytorkhov.blogspot.co.uk/2009/09/mounting-raw-and-qcow2-vm-disk-images.html)
losetup /dev/loop0 image.img
kpartx -a /dev/loop0
mount /dev/mapper/loop0p1 /mnt/image
Mount qcow2 (same place)
modprobe nbd max_part=63
qemu-nbd -c /dev/nbd0 image.img
mount /dev/nbd0p1 /mnt/image
(if lvm is present)
vgscan
vgchange -ay
mount /dev/VolGroupName/LogVolName /mnt/image
and finishing
umount /mnt/image
vgchange -an VolGroupName
killall qemu-nbd
kpartx -d /dev/loop0
losetup -d /dev/loop0