I highly suggest you use the Geo-matic iframe from
www.crakrevenue.com
We've developped an awesome tool that can automatically present the best converting product based on your traffic's GEO IP location. Never mind switching ads manually, now you can set and forget your campaigns and concentrate solely and getting more traffic - we'll take care of converting it.
All you need to do is copy this iframe code to your site and we will take care of displaying geo-targetted ads to your traffic.We only show the top converting banners for your visitor's country. Before adding a banner to our system, we test it with our own in-house traffic and tweak each design for optimal CTR.
http://crakrevenue.com/geo_tools