http://147.8.93.173/magicstudio/index.htm

Magic VC7ToVC6 can automatically convert Visual C++ 7.x projects back to Visual C++ 6.0 projects.

In other words, * .sln -> *.dsw or * .vcproj -> .dsp .

Important note, there is no loss during the conversion: source code is left unchanged; only .dsw / .dsp are created (or overwritten).

Actually there are several scenarios where this tool is useful:

Someone gives you a VC++ 7.* project, and you only have VC++ 6 installed.
You have upgraded your project(s) from VC++ 6 to VC++ 7, and you have both .dsw / .dsp and .sln / .vcproj files on your local system drive, but you are willing to keep those files synchronized so any time you need to open the project, you need not bother the VC++ version you work with.
Provide both versions of projects ,so your audience does not need to bother with knowing which devtool is required.