If the nail is in the sidewall, the tire is likely toast. However, if the nail only penetrated the tread, many tire shops will fix the flat for free, even if they don't sell that particular brand of tire! Always a nice way to get you to consider them the next time your in the market for tires. I've experienced this from Les Schwab (west coast) and Big-O tire dealers.
Just got a nail in my tire. Arrgggg!!!! Don't suppose there is some sort of coverage for that?