If you need interop assemblies for .NET:
If you are a .NET developer (C#, VB.NET) and need the library for Visual Studio, you should not reference EXCEL.EXE directly. Instead, install the official Primary Interop Assemblies (PIAs).
Note: The PIA download is for developers deploying applications. It does not let you run VBA macros without Office installed.
Short answer: No. Microsoft does not distribute the Excel 12.0 Object Library (EXCEL.EXE) as a separate, legal download.
The library is embedded within the core Excel 2007 installation. If you need it, you must have access to: