Ambien: get a new set of wheels dude. For one 18" snow tires are going to be expensive, and if you figure $80 to mount the summer tires each spring, and $80 to mount the snows, thats $160 a year, plus the fact that those tire jockeys are going to crunk up your wheels ripping tires off two times a year. Also it is bad for the tires to be ripped off so many times, and you don't want that winter salt on your nice 18's. Finally you can get some more narrow tires to help cut through the snow, with a bigger side wall to, like xmas said, accept those nice big pots holes we get in the winter.
edit: i almost forgot an big one, you can put mount the snows yourself if you get another set of wheels. the big advantage of that is the conveniece, beacuse if you get one big snow storm and put your snows on, then its 65 degrees and sunny for two weeks and everything melts then you are wearing your snows down hardcore. with another set of wheels you can just put your summer tires back on until the next snow frenzy.