Regarding the battery issue:
In my experience the Canon Li-ion batteries have done well in the cold. I would MUCH rather have the proprietary rechargable batteries than AAs because they are lighter, smaller, last longer, do well in the cold, and they are very cheap.
You can buy Li-ion batteries for the canon SD series on ebay for about $5 each. At that price, buy 6 of them, charge them all up, and take them on a month-long cold weather trip. No worries about battery problems.
The SD series is so small its comfortable to keep it on a lanyard around your neck inside your jacket (quick access!), so cold batteries shouldn't really be much of an issue anyway.
I've had the sd400 and now have the sd600 and will soon be getting the sd800 (when I find a good enough deal).