Tyre / tire size

I had another look and I have about 1cm of clearance on the front, but the back is not as easy - not only would the mudgurad have to come off, but it might even catch the frame.
I think I'm going to have to visit a better bike shop which actually stocks winter tyres. I remember the guy laughed a little when I said that I would ride through winter last year. Pissed me off already 3 times giving me shit, or the wrong size parts. Only problem is finding somewhere.

Thanks for the links, I'll read up a bit and when I end up getting some I'll be back.
Thanks

I'm in Poland, and last year we had plenty of snow, which in some places was cleared and in others not.

I remove my full mudguards and put crud catchers on. Ugly as... but keeps the wet snow off my botty. You need to find a shop that'll let you try out a winter marathon, as it might fit.