Lex Jenkins , Jan 29, 2009; 06:36 p.m.
Regarding your first question...
Snow scenes in daylight are typically around EV 14-16. Since the Holga is limited in exposure settings to a shutter speed of 1/125 second and f/8 or f/11 (going by manufacturer specs, I don't own a Holga), you'll need to choose a film to suit the conditions. The Holga is modeled after the simple camera designs of decades ago when film speeds were typically much slower.
An ISO 400 film is too fast for those conditions - bright daylight reflected from snow with a camera having limited exposure options. Your photos will be overexposed. The negatives will appear "too dark."
For those conditions with a Holga choose an ISO 100 or slower film. Kodak T-Max 100, Ilford FP4+ or Pan F+ (ISO 50). I'd choose Ilford FP4+ for its flexibility. While nominally an ISO 125 film, it delivers good results from ISO 50-250 with careful processing.