I just looked up a Deskstar datasheet, and it specifies 5C to 60C operating, -40 to 70C non-operating. WD Caviar is 0-60C operating. Looks like it would be best to not freeze your hard drive.
It sounds like if the fans stop working, that would actually be what you want to keep the system warm...
2. Materials generally lag tracking the ambient temperature, which means that the drive will be colder than its surroundings when it get warmer, so a shit load of water may condense out on the electronics/inside the drives.
I'm pretty sure some of the drives I've split open have had dessicant inside. Dunno if it'd be enough with that much delta T though. Depends on the humidity too I suppose.