Qt Currency Converter Client

I want to create a Currency Converter Client application in Qt that provides you with up-to-date currency exchange rates from the Internet using the Yahoo API, and therefore allows you to convert between many worldwide currencies. The program should allow you to perform multiple currency conversions at the same time. Additionally, the application should store the last conversion rates retrieved so that you can use it offline if needed. It should also work from behind a proxy server. I developed this application using C# on .NET, but i would like to create a C++ Qt version of it, to be able to run it cross platform, so i really prefer someone with great Qt knowledge! The application should also have an installer Screenshots of the application i wrote are available.