Guys, let me share you my experience with IS 250 auto on snow.
In 2009, we had the first snow in December for the last couple of years. Obviously, I was not equipped with winter tyres, so after a good half an hour trying to take the car out of my garage, I surrendered myself and put it back (very difficult as well).
I installed 4 Nokian WR G2 (225 45 17 in front and 245 45 17 for the rear, all with alloy wheels). They are not really winter tyres, although they are marketed as both winter and summer (though they do not mention the words 'all season'). They are really incredible, on snow, ice, slush, you name it. Of course they tend to be a little bit noisy, but it only bothers me after 100 kmph. I climbed hills with them, drove on other people's tracks, went to the mountains and they proved really useful.
However, I found myself in 2 rather difficult situations:
1. a couple of days ago, when trying to turn on a narrow street surrounded by snow, I found myself unable to move because there was ice under the rear wheels, and lots of snow under the engine and the front part. It took me half an hour to be able to do something (the car was also perpendicular on the road, so pushing it was still difficult).
2. this morning, when my car was parked outside on old snow (flat terrain), and it snowed quite a lot (approx. 20-25 cm of fresh snow for the last 7 hours; I was at a mountain resort). I completely cleaned the car (I am a freak when it comes to that, and I would not allow myself to drive with snow on it), but I was unable to get it to move. With the help of a shovel and some good push, my girlfriend did move it about 1 meter behind, but that was it. Once a Range Rover SUV towed me to the tracks left by other cars, I was able to drive it. It could also be the fact that it's a very low car, with automatic gearbox.
Bottom of line is good tyres help you a lot (before, even on slush, i was able to drive with max. 30 kmph, since the car was almost uncontrollable), but they don't help you all the time. Studded tyres could be a solution, but they are forbidden to use here (I think they are allowed in rally competitions, but not on roads). Chains (I hear RUG has some very good ones) are also something to consider.
Good luck to everyone in snowy conditions out there.