Marta, I haven't done much winter sowing either, but I think the snow cover on them is actually supposed to be a good thing. I know that critterologist and greenthumb have done quite a bit of winter sowing and I'd be glad to coax them to talk about it to our hearts content when we get together for the seed swap next weekend
Also, I'm going to go check out critter's articles on DG - knowing her, there is probably an article or two she has written about it