The product which would allow you to create dynamic QuarkXPress files, and modify text, images, and their formatting, is QuarkXPress Server. QuarkXPress Server and its companion component, QuarkXPress Server Manager, expose an interface for modifying documents through Web Services, and can be referenced as a web reference from a C# Visual Studio.Net project.
To use this functionality, you must first set up QuarkXPress Server and QuarkXPress Server Manager (I wont describe that here, theres installation instructions provided with the software), and have both applications running on your server. Once set up, you can add a new web reference into your C# project, and, when prompted, use the URL: http://:/
(where and represent the server IP address and port number of the server where QuarkXPress Server Manager is running a default installation would be: http://localhost:8090/quark/services/qxpsmsdk?wsdl
You should then also give the web reference an appropriate name something like quarksdk, and click add. Once the web reference is added, add a using reference (for example, using quarksdk) at the head of your projects main .cs file. This will now give you access to the QuarkXPress Server Manager SDK as a web service through your project. Full details of how this service can be used are provided in the Web Integration Guide provided along with the software.
Hope this information is helpful.