Maurice - 11:23 am on Jul 26, 2010 (gmt 0)
well as IP's are handed out on a country level and not a state, county, province level (IP is not like NANP or telecoms number schemes) - your probably not going to get a 100% accurate solution.
As people have said you can buy access to gelocation lists which you could use to block particular IP's
Id also block it at the exterior router if possible as using htacess will still put an additional load on your webserver.
Do you really need to do this? aren't there laws about interfering with interstate commerce in the USA?