1. It's really quite easy to make a new Ubuntu installation over an existing encrypted LVM:
- copy your /etc/crypttab to /home,
- boot from an alternate install CD into the rescue mode,
- give the passphrase when the installer asks for it, use the partitioner in the normal way, install,
- boot from an alternate install CD into the rescue mode, again,
- copy the crypttab from /home back to /etc/crypttab,
- update-initramfs -k all -c -v,
- happy happy joy joy.
2. If your laptop's (in this case Dell Latitude E6400) screen suddenly goes black when you activate some display manager, and does not react to anything at all, try taking the damn thing off the docking station. Then boot it, find the power management setting and fix it so that it doesn't do it anymore (in this case, told it not to react to AC poweror closed lid).