The DIALOGS.RES and DIALOGS.H files are created by the Dialog Editor. Together they are an archive of all the dialog information. The .RES file contains all the dialog information except the symbolic names you've defined, which are in the .H file.
Don't confuse the .RES file written by the Dialog Editor with the .RES file produced by the Resource Compiler that is linked into your application. The .RES file that the Dialog Editor writes is just an archive for the Dialog Editor's use.
Note You must avoid name conflicts between the two .RES files. Failing to avoid name conflicts will cause unpredictable results.