Yes and no. It depends how portable you want it to be. If you can live with running it on Windows/IE only, you can implement your application as an ActiveX component. If you want it to be a bit more portable, you can implement it using Jambi and embed into the webpage using the webstart technology. But if you want it to be really portable, you have to build your application for each platform separately and allow a regular download of an installation package from your website.