Are you saying you want to refurbish the website, or make the website available as client-side software?
To update the website, I would recommend using AJAX for automatic client-side calculations with javascript (which will obtain the results from server-side scripting in PHP)
If you want to write client-side software, I would recommend Delphi, as its database connectivity is considerably good, with C++ being a secondary option due to its flexibility in overall design.