I think the P-Zero's are the problem.
I was getting loads of rear wheel spin with those, even in slightly damp conditions.
Changed em for Eagle F1's - not had those problems since.
Not driven in the snow with them though.
Yes - it was that bad Brett, but then again, this is a reasonably powerful, rear wheel drive car, on big, wide, low profile summer tyres - not the best combination for driving in the snow.