ADD-IN for Office 2007 and IE 7.0 for Windows VISTA using .NET

We need to develope a ADD-In / Plug In which shall work as follows: When you select a word e.g. Apple in Microsoft Word (Office 2007), Excel (Office 2007) or Internet Explorer 7.0 along with usual Right Click menu a new Menu option shall be available which will translate the selected word (Apple) in any another language. Code to translate will be provided. We need code to add a new option to Right Click menu. MUST be developed using .NET ad work under VISTA. Kindly quote if you know how to work with VISTA