Volvo dealers will start selling winter wheel/tire packages soon, if they havent already. I picked up a set a few years ago, four steel rims, four Gislaved NordFrost II tires, and four Volvo wheel covers for $699 Canadian. The tires have an agressive tread pattern that really bites into the snow, and can be studded if they allow it where you live. The recomended size for your car is 185/65/15. I'd stick with that size if possible, a narrower tire is allways better in the snow to help it bite through and prevent it from "floating" on top. Most winter tires (including the Gislaveds) have a softer sidewall, so you won't lose any ride comfort. If you want to look elsewhere for wheels, tirerack.com sells winter wheel/tire combos for your car, as will many large tire stores. They use generic wheels with multiple bolt patterns to fit more than one application. Your other options include E-Bay, and wrecking yards for used wheels. There were a lot of 850's/S70's/V70's sold from 1994-2000 with steel wheels, and they will all fit your car.
Good luck.

Koz.