There are two main components that you need:
Version 2.0 or higher of the Microsoft .NET Framework software development kit. You will need the full software development kit, not just the redistributable package. The .NET Framework software development kit includes the C# compiler (csc.exe) and a set of classes that are used at runtime during decode and encode operations. The Xbinder C# functionality was tested with version 2.0 of the .NET Framework.
XBinder C# Runtime (xbrt.dll and xbrt.snk). The DLL needs to be referenced when compiling and in a location where it can be found at runtime. If you copy the DLL to another location before compiling against it, you will also need to copy the .snk file. At runtime one way to ensure that the file is found is to copy xbrt.dll into the same folder as the .exe that is referencing it. Another way is to add xbrt.dll to the global assembly cache via the gacutil.exe program. Other mechanisms might also be available via application configuration files; consult the appropriate Microsoft documentation for the development tool you're using.
You can obtain the Microsoft .NET Framework via the download center on the Microsoft web site (www.microsoft.com). Depending on the version you select, the words “software development kit” may or may not be specified with the selection on the web site. But the words “redistributable package” are consistently used for kits that contain just runtime components. You will want the software development kit, not the redistributable package.
If Microsoft Visual Studio 2005 or higher is installed on the machine where you will be using the Xbinder C# compiler, then you already have at least version 2.0 of the Microsoft .NET Framework. The Microsoft .NET Framework is typically installed into the \WINDOWS\Microsoft.NET\Framework folder; you can probably check this location to see if you already have it. You can also search for csc.exe to see if you already have the Microsoft C# compiler.