Search the forums. This one's been addressed a couple times.
Is your area just cold, or is it cold and snowy? If snowy, then it will be quit humid at times too. How sealed is your garage? Does water seep in when it rains or snow melts?
For me, I kept a Galaga in the garage for 1 winter. I will never do that again. Though it still worked fine after ward, many metal parts that were not rusted before, now were. Rust had appeared on the back of the CP, and the vent grills near the bottom were completely rusted and my fuse clips rusted too (enough so that when I eventually had to replace the fuse block because the fuses stopped making proper contact).
Some people say wrap the cabinet in plastic.
Some say take the electronics and monitor out of it and keep those parts in-door. Some say you'll be fine...