I want to setup a site where all visitors from the US are accepted and all others are denied and brought to a seperate page (ultimately so I get the maximum adsense click). However, I have absolutely no idea as to how to setup this up, I only assume it's possible. Any help would be much appreciated
Take a look at Mixmind MaxMind - GeoLite Country | Open Source IP Address to Country Database. Their software determines the visitor's country code using their ip address. I currently use it with php. It's pretty straight forward, you just download their database file and php script and integrate it into your site. Best of all, their GeoLite Country version is free.