+1 to treebound

I used to ride a crappy mtb as my winter bike. I rode it through 5 winters. It's the salt and sand that get's ya. The sand eats away at your gears and chain and the salt gets into your components and goes bad until you gotta lop 'em off at the wrist. (Who's laughing now lx rear der? muahaha). I converted the bike to singlespeed to avoid having to deal with shifters that wouldn't shift and derailleurs that needed to be demucked nightly. I didn't feel like riding my "nice" bike through the crap because I felt like every bit of salt and every grain of sand took a few days off the life of my beloved.

However, treebound is right. If you keep on top of maintenance and cleaning then you'll do fine. Be especially sure to clean the chain, cogs, and chainring every day, and your drivetrain should make it through without too much trouble.

Your old fixie might be a good simple winter ride, though. A lot of people around here switch to fixies during winter because they feel they can control the bike better. What kind of parts were you thinking you need to buy for it?