A lesson learned: in order to mount an LVM device on another machine or simply another OS (e.g., from within a live cd os, mount the local machine's volumes), the LVM volume group must be exported and then imported. This is done using the vgexport / vgimport commands.
Another requirement, is to have lvm2 package installed (so lvs command actually sees the volumes), and device mapper module should be loaded (dm-mod) or builtin the kernel.
Thanks for Amir who found that out.
By the way, I've recently found the dmsetup command very useful.