Atlanta has the best rushing game in the league so I think it will still be a problem even in the cold. I would imagine that it will try and keep Vick from passing much and make sure that he is protected with quick throws, roll outs and lots of running. They may have some problems holding on to the ball though and it so I would thing the Bears will win.
Looks like the temperature is expected to be around twenty. While I know the colder it gets the worse for the Falcons but also the worse for my feet.
Have fun! Stay warm...
Regards,