In a VirtualBox VM I tried to install Debian Lenny on a system using LVM2 mirroring to see if I could get it to work.

Before I got to the partition drives option I switched to a shell and fdisked the two virtual drives and set them up as software raid for the boot partition and the rest of the drives as LVM containers. I then did a modprobe for the device mapper, a pvcreate, a vgcreate and two lvcreates with mirror option. In theory the LVM system should manage mirroring of the logical volumes it created. I did a varyon, then I laid down ext3 filesystems and mkswap and was even able to mount/umount them okay.

Back in the DI installer I then tried to use my new filesystems that had been created. The installer detected the filesystem layout and was happy to let me choose the mount mounts for boot, root and nominate the swap partition. I hit continue and I briefly saw some error message before it threw me back at the partition stage. I couldn't find the error message on any of the virtual consoles, or I'd had Googled for it.

Looks like I'll have to stick with the traditional software mirror first before applying the LVM on top.