I need to develop a mobi site for a client, do I need a specific server setup for this, or are there any additional server configurations that I need in order to render a mobi site or does it work the same as a normal website?
A .mobi domain is not different (in terms of setup/configuration) than a .com
Even from a technological point of view, you can develop a mobile oriented application using the web technology (Java, PHP, Python, PHP...) and hardware infrastructure you prefer.
From the developer perspective, there's good instructions for .mobi compliance here, and ready.mobi is a great and free testing tool to evaluate mobile-readiness using industry best practices & standards.
I believe that you should check the availability of Javascript in the target platforms.
ready.mobi is a great tool for testing compliance for this. Also, there's good instructions for .mobi compliance here.
Your server should be able to serve pages with the application/vnd.wap.xhtml+xml MIME type, otherwise some WAP browsers wil not render the page correctly (Nokia series 60).