Ok this is tricky but possible.
This is the way I would go about doing it.
1) Retrive users IP address
2) use a whois and get information about the users location
3) Redirct them using header("location:$country");
This is a good idea and a bad idea, it is quite possible. But there are so many isps out there that you really can't be sure of which country or location a user is in. It might be better to let the user select which area he is in.