I'd start with St. Sheldon:
http://sheldonbrown.com/tire-sizing.html

Essentially, 700C is a size, with a 622 bead seat diameter. 38mm is how wide the tire is.

Winterizing, I got studded snow tires. But I live in Minnesota.

I think the zip ties work if you don't have rim brakes. I've met a lot of folks that just put a studded tire in front, but every fall I've had in winter (there's been a few) the rear tire skids out from under me.