No idea how to help here as I always just do a clean install of vector in the first place, i.e. I long ago divided my HD into a root, home and swap partition. When I install VL 7, I leave my home partition alone (don't reformat it). I install VL 7 in the root partition. That works going from VL 6 to VL 7. No clue what to do when going from Ubuntu to VL7.