I have had the same problem with a 2002 X-5 3.01 and the 2005 X-5 4.41 sports model I have now. Recently I drove a loaner X-3 and a 2009 X-5 that handled incredibly well in the snow. I can't figure it out. My previous Honda Accord with front wheel drive handled better than the X-5 I have now. My tires are new...Michelin Diamaris and I'm not using nitrogen. In the snow my X-5 fishtails during turns (even at very slow speeds) and stopping is a long process. It's frustrating as I watch other vehicles and I seem to be the only one having difficulty. And yes, I know how to drive in the snow.
I spoke with BMW service, they told me to buy snow tires. I don't want to pay $1200 for tires and then mounting fees twice a year.
If any one has any suggestions I'd love to hear. Otherwise thanks for letting me vent. - Pat Striplin