In my project I (did) have two .rc files. When I compile and run the menu doesn't show up and my about dialog won't work.
If I have one .rc file with both the menu and dialog code it works perfectly. This was not a problem with Dev-C++ (I had two .rc files) but maybe this is a problem with the resource compiler.
Here is what didn't work.
menu.rc
#include <windows.h>
#include "main.h"
IDM_MENU MENU
{
    POPUP "&File"
    {
	MENUITEM "&New\tCtrl+N", IDM_FILE_NEW
	MENUITEM "&Open\tCtrl+O", IDM_FILE_OPEN
	MENUITEM "&Save\tCtrl+S", IDM_FILE_SAVE
	MENUITEM "&Save as...", IDM_FILE_SAVEAS
	MENUITEM SEPARATOR
	MENUITEM "&Page Setup...", IDM_FILE_PAGESETUP
	MENUITEM "&Print\tCtrl+P", IDM_FILE_PRINT
	MENUITEM SEPARATOR
	MENUITEM "&Exit\tAlt+F4", IDM_FILE_EXIT
    }
    
    POPUP "&Edit"
    {
    	MENUITEM "&Undo\tCtrl+Z", IDM_EDIT_UNDO
    	MENUITEM SEPARATOR
    	MENUITEM "&Cut\tCtrl+X", IDM_EDIT_CUT
    	MENUITEM "&Copy\tCtrl+C", IDM_EDIT_COPY
    	MENUITEM "&Paste\tCtrl+V", IDM_EDIT_PASTE
    	MENUITEM "&Delete\tDel", IDM_EDIT_DELETE
    	MENUITEM SEPARATOR
    	MENUITEM "&Select all\tCtrl+A", IDM_EDIT_SELECTALL    	
    }
    
    POPUP "&Search"
    {
    	MENUITEM "&Find\tCtrl+F", IDM_SEARCH_FIND
    	MENUITEM "&Find next\tF3", IDM_SEARCH_FINDNEXT
    	MENUITEM "&Find previous\tShift+F3", IDM_SEARCH_FINDPREVIOUS
    	MENUITEM SEPARATOR
    	MENUITEM "&Replace\tCtrl+R", IDM_SEARCH_REPLACE
    }
    
    POPUP "F&ormat"
    {
    	MENUITEM "&Word Wrap", IDM_FORMAT_WORDWRAP
    	MENUITEM "&Font...", IDM_FORMAT_FONT
    }
    	
    POPUP "&Help"
    {
	MENUITEM "&Contents\tF1", IDM_HELP_CONTENTS
	MENUITEM "&Search", IDM_HELP_SEARCH
	MENUITEM "&Using help", IDM_HELP_HELP
	MENUITEM SEPARATOR
	MENUITEM "&About...", IDM_HELP_ABOUT
    }
}
dialog.rc
#include <windows.h>
#include "main.h"
#ifndef IDC_STATIC
#define IDC_STATIC -1
#endif
IDD_ABOUT DIALOG 0, 0, 239, 66
STYLE WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "Text Editor 0.1.1.1"
FONT 8, "MS Sans Serif"
{
	DEFPUSHBUTTON "&OK", IDOK, 174, 18, 50, 14
	PUSHBUTTON "&Cancel", IDCANCEL, 174, 35, 50, 14
	GROUPBOX "About this program...", IDC_STATIC, 7, 7, 225, 52
	CTEXT "This is a simple text editor written in C++.\r\n"
	      "The GUI was created with the Win32 API.",
	      IDC_STATIC, 16, 18, 144, 33
}
Here is the code I used that worked.
resources.rc
#include <windows.h>
#include "main.h"
#ifndef IDC_STATIC
#define IDC_STATIC -1
#endif
IDM_MENU MENU
{
    POPUP "&File"
   {
	MENUITEM "&New\tCtrl+N", IDM_FILE_NEW
	MENUITEM "&Open\tCtrl+O", IDM_FILE_OPEN
	MENUITEM "&Save\tCtrl+S", IDM_FILE_SAVE
	MENUITEM "&Save as...", IDM_FILE_SAVEAS
	MENUITEM SEPARATOR
	MENUITEM "&Page Setup...", IDM_FILE_PAGESETUP
	MENUITEM "&Print\tCtrl+P", IDM_FILE_PRINT
	MENUITEM SEPARATOR
	MENUITEM "&Exit\tAlt+F4", IDM_FILE_EXIT
    }
    
    POPUP "&Edit"
    {
    	MENUITEM "&Undo\tCtrl+Z", IDM_EDIT_UNDO
    	MENUITEM SEPARATOR
    	MENUITEM "&Cut\tCtrl+X", IDM_EDIT_CUT
    	MENUITEM "&Copy\tCtrl+C", IDM_EDIT_COPY
    	MENUITEM "&Paste\tCtrl+V", IDM_EDIT_PASTE
    	MENUITEM "&Delete\tDel", IDM_EDIT_DELETE
    	MENUITEM SEPARATOR
    	MENUITEM "&Select all\tCtrl+A", IDM_EDIT_SELECTALL    	
    }
    
    POPUP "&Search"
    {
    	MENUITEM "&Find\tCtrl+F", IDM_SEARCH_FIND
    	MENUITEM "&Find next\tF3", IDM_SEARCH_FINDNEXT
    	MENUITEM "&Find previous\tShift+F3", IDM_SEARCH_FINDPREVIOUS
    	MENUITEM SEPARATOR
    	MENUITEM "&Replace\tCtrl+R", IDM_SEARCH_REPLACE
    }
    
    POPUP "F&ormat"
    {
    	MENUITEM "&Word Wrap", IDM_FORMAT_WORDWRAP
    	MENUITEM "&Font...", IDM_FORMAT_FONT
    }
    	
    POPUP "&Help"
    {
	MENUITEM "&Contents\tF1", IDM_HELP_CONTENTS
	MENUITEM "&Search", IDM_HELP_SEARCH
	MENUITEM "&Using help", IDM_HELP_HELP
	MENUITEM SEPARATOR
	MENUITEM "&About...", IDM_HELP_ABOUT
    }
}
IDD_ABOUT DIALOG 0, 0, 239, 66
STYLE WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "Text Editor 0.1.1.1"
FONT 8, "MS Sans Serif"
{
	DEFPUSHBUTTON "&OK", IDOK, 174, 18, 50, 14
	PUSHBUTTON "&Cancel", IDCANCEL, 174, 35, 50, 14
	GROUPBOX "About this program...", IDC_STATIC, 7, 7, 225, 52
	CTEXT "This is a simple text editor written in C++.\r\n"
	      "The GUI was created with the Win32 API.",
	      IDC_STATIC, 16, 18, 144, 33
}