a little more thought
Thanks for the tips everyone.
Upon reflection, I probably would use the sourcebooks promarily for DM information -- Monsters, envirnment effects, NPCs etc. I would make the rules in Frostburn standard rules for most things, and add good flavor stuff from Frost and Fur.
I would probably allow players with the sourcebooks to use the feats, spells, classs if they want, but I would have to be careful about what to allow from Frost and Fur. I'd keep a limit on it.
I have GURPS Russia, I'll be using that for some inspiration.