Fun fact: unless you're right on top of Ground Zero, you're probably going to be alright. If I recall the defense article correctly, 24-48 hours in a basement will be enough time for the worst of the radiation to disperse, and you can go outside and head to wherever you need to go that's in the opposite direction of the blast.
EDIT: This isn't the link I was thinking of, but it's still good.
Yay, learning! 80% of the fallout should disperse within the first 24 hours. Obviously, being downwind is going to suck more.
EDIT II: So yeah, I concur, 'Fallout' Fallout Shelters probably aren't the safest bet thanks to Vault Tech's villainy.