I documented how to do this with RAID5 on this page:
http://www.gagme.com/greg/linux/raid-lvm.php
There is a possibility to make LVM on top of RAID-{0,1,5}
If you need mirroring, use RAID1 array and then make LVM on top of this array.
-- Greg Gulik http://www.gulik.org/greg/ greg @ gulik.org