If you're keeping the car long enough, it might be cheaper to buy winter wheels. You can get 18x8" wheels to fit your car from Tire Rack. Here's a thread on swapping the wheels yourself.
http://www.1addicts.com/forums/showthread.php?t=367142
If you don't want to swap the wheels yourself, or if you want to put the winter tires on your stock wheels, you can easily fit all four wheels or tires in your car if you fold the rear seat down.