I have a script that will do it for you in php, and
Cash 4 China has an asp version.
I think personally that the script options are actually a better bet...most of the geoIP server mods I've had experience with have horribly innaccurate ip databases that are outdated and not truly effective.
I feel that browser language is personally the better bet...I imagine you can do it by system language too, which might be effective as well.
Let me know if I can help in anyway, we replaced the chinese dialers on amateurpages with
Cash 4 China and have so far had good results.