One very important thing to remember with chains is that they have pretty serious usage limits. DO NOT drive over 35-40km/h with them, and DO NOT drive on bare pavement with them unless you want to destroy your tires.
They're handy to get you out of a pinch, but winter/snow/ice tires are far preferable if you're going to do any serious amount of winter driving.
There's a great article comparing different types of "winter tires" here:
http://www.theglobeandmail.com/servl...cialGlobeAuto/