Over the last 4 months or so, I have shot maybe 20 rolls of 120 and 35mm, all in snowy conditions. It's a condition of living where I do!!!

The simplest solution is to use an incident meter. If you haven't got a hand-held meter, use sunny-16. If you only have a built-in reflective meter, compensate at least one stop, if not two, depending upon how dark your subject is. I've used both Delta-400 and FP4+ with great success in snowy conditions.

Basically, don't trust reflective readings and you should be OK.

Hope this helps,