For new work, I would recommend using Visual Studio .NET 2008. Use the Express edition if you can't afford to buy one. VS.NET has a vastly improved standard C++ library as well as a vastly improved compiler.
VS.NET can open VC6 project files (.dsp) and workspace files (.dsw) and converts them to use the appropriate solution/project file that goes with the edition of VS.NET. Any changes you make in VS.NET will only be reflected in the upgraded version of the project (.vcproj) and solution (.sln) files. However, if you need to backfill them into a VC6 project file, you can open the .dsp/.dsw in the text editor (use Open with...) and be saved out.
VS.NET (or Visual C++ Express) can compile native code and managed C++/CLI code, it is not just for .NET projects despite .NET being in the name.