In reply to filip.kamycki:
http://www.ukclimbing.com/forums/t.php?t=566026
That was my thread from last year. Lots of good advice and websites. The daylight won't be a problem. We only had 4 hours or so of sun up, but there was 2-3 hours of useful twilight each side of that.
We hired a Jeep Wrangler from Geysir rentals, it was brilliant, but didn't have studded tires, and off the main roads most of the roads were sheet ice which was ok, but we spun a couple of times once on a descent and once in a strong crosswind. So if you plan to go off Highway 1 you had better have good driving nerves!
Driving at night was difficult, there were regular drifts over the road of a few inches thick on top of the sheet ice.
Wind was a bigger problem in getting around than anything else, we planned on driving along the south coast, but it wasn't possible because of the crosswind, so had to book into our apartment for a few more nights.
Get hold of the rough guide, or LP and be realistic about how much driving you want to do, you won't be able to drive fast if it's cold and windy and dark. We found really nice apartment accomodation for about £70pn for a double, hostel in the capital for about £20pppn. Dinner in restaurants was about the same as you would pay in the UK outside of london. Groceries were again about the same as the uk if you stick to the cheap supermarkets.
Walking was ok on the main paths in the valleys, but we wanted crampons to get up to some of the higher ground.
Microspikes (little crampon type things) were brilliant for walking around looking at waterfalls etc, we could get to loads of places that the bus loads of tourists couldn't get to.
Northern Lights spotting was hard work on our own, cold and lots of waiting around and driving at night, but would have been much more rewarding that being with one of the bus tours from the capital which was a bit like a cattle market. (had we seen any)
Good luck. It's brilliant. I can't wait to go back.