Some steps in the DDK installation require that you run the utilities you installed in a previous step. To ensure that the correct utility is run, add the WINDEV directory to your PATH environment variable before starting the installation. Since existing utilities on your hard drive may conflict with the DDK utilities, make sure the WINDEV directory is placed before any other directory, including the MS-DOS directory. If you have directories containing tools from previous versions of the Windows DDK, it is a good idea to remove those directories from the PATH variable.
Although the INCLUDE and LIB environment variables are not used during installation, you should add the WINDEV\INCLUDE and WINDEV\LIB directories to them. Again, if you have directories containing header files or libraries from previous versions of the Windows DDK, it is a good idea to remove those directories from the INCLUDE and LIB environment variables.
Finally, you should make these changes permanent by modifying the MS-DOS path and set commands in your AUTOEXEC.BAT file.