The application has to run on Linux and replicate the look, feel and functionality of the original ASP.NET application. How you get there is up to you, but some suggested methods are:
Use Mainsoft's Grasshopper.This is a free plug-in for Visual Studio .NET which enables you to use C# or Visual Basic .NETŪ to develop, debug and deploy Web applications and Web services that run on Microsoft Windows, Linux and any Java-enabled platform. If you think taking your application, hitting F5 and having your application compile to Java byte-code sounds like an easy way to port then this could be the method for you. Some seasoning to taste may be required.
Port directly to Mono. Mono provides the necessary software to develop and run .NET client and server applications on Linux, Solaris, Mac OS X, Windows, and Unix. Mono is multi-platform, based on the ECMA/ISO standards, can run .NET, Java, Python and more, and is Free Software. If you enjoy porting C# to other .NET implementations then this is right up your alley.
Rewrite using PHP. PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. PHP is free and available for many different platforms. If you're comfortable with PHP and like rewriting code then this could be the challenge you've been looking for.
Use a Macromedia product. ColdFusion, or Flash will get you up and running but, like PHP, will require a complete rewrite of the applications. If you're a magician with Macromedia then go for it.
These are merely suggestions. Be the first to have an application running on Linux that replicates the ASP.NET version and you've won yourself an Xbox.
Bonk, they said PHP....mmmmmm....