You should download Knoppix V3.8.1 (2.6 kernel) or the older Knoppix V3.7 (2.4 kernel + experimental 2.6 kernel) and see if it can mount the LVM. See http://www.knopper.net/knoppix/index-en.html
for download info. The older V3.7 worked fine under the 2.6 kernel, but I have had problems getting the V3.8.1 to run properly.
Knoppix is a full featured, self-booting linux CD that runs in KDE. Think of it as “linux rescue” on steroids. Not only could you use it as your regular version of linux, but it is also great for fixing dead systems or for addressing problems like you are facing.
Disclaimer: I have no personal experience using Knoppix to mount an LVM.