A growing number of third party software has already included wikipedia data somehow. It starts with trillian, there is a wikipedia widget for MacOS X and one company with friendly relations to Wikimedia (Answers.com) has released a tool. Not to forget Babylon.

One tool with is missing support for wikipedia data is currently Google Desktop. Version 4 was released hours ago and the company is trying to catch up in terms of the number of gadgets offered by announcing a contest for creating these. Details can befound at http://desktop.google.com/contest.html. There is also an IDE for development at http://desktop.google.com/designer.html a documentation for the SDK at http://desktop.google.com/developer.html.

Maybe someone is interested in this challenge.