Quick question - I kind of assume that a fire breathing dragon resists fire, and a frost breathing dragon resists frost, etc. Is this assumption correct? I suppose some dragons (I've not encountered an Elder Dragon yet, but I've heard of them) might resist all magic, but do even the basic dragons resist their own attack type?

I believe all dragons resist a percentage of their own damage type, and are weak to the opposing damage type. Shock is always straight up, never boosted or resisted.

http://www.uesp.net/wiki/Skyrim:Dragon