Hosting same web site in different geo-l

I am in the process of hosting an E-commerce site on a server running NT4.0 and IIS located in the US. I would like to maintain the same site on other servers located at other geographical locations across the globe. Suppose a surfer tries my URL from USA, he will go to my US server, but when another tries it from Australia, it will go to my Australia server. How can I achieve this? Any help would be highly appreciated.

Regards,

Sarkar