Last part of fix for bug #8562 with Emacs on Windows 9X.

 nt/runemacs.c (ensure_unicows_dll): New function, tries to load
 UNICOWS.DLL on Windows 9X.
 (WinMain): If ensure_unicows_dll fails to find UNICOWS.DLL,
 display a dialog to the effect that Emacs cannot be started.

nt/ChangeLog

+2011-11-04  Eli Zaretskii  <eliz@gnu.org>
+
+	* runemacs.c (ensure_unicows_dll): New function, tries to load
+	UNICOWS.DLL on Windows 9X.
+	(WinMain): If ensure_unicows_dll fails to find UNICOWS.DLL,
+	display a dialog to the effect that Emacs cannot be started.
+	(Bug#8562)
+
 2011-10-28  Eli Zaretskii  <eliz@gnu.org>
 
 	* README.W32: Mention UNICOWS.DLL as prerequisite for running

nt/runemacs.c

@@ -45,6 +45,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <malloc.h>
 
 static void set_user_model_id (void);
+static int ensure_unicows_dll (void);
 
 int WINAPI
 WinMain (HINSTANCE hSelf, HINSTANCE hPrev, LPSTR cmdline, int nShow)
@@ -59,6 +60,9 @@ WinMain (HINSTANCE hSelf, HINSTANCE hPrev, LPSTR cmdline, int nShow)
   char *p;
   char modname[MAX_PATH];
 
+  if (!ensure_unicows_dll ())
+    goto error;
+
   set_user_model_id ();
 
   if (!GetModuleFileName (NULL, modname, MAX_PATH))
@@ -203,3 +207,43 @@ set_user_model_id (void)
     }
 }
 
+static int
+ensure_unicows_dll (void)
+{
+  OSVERSIONINFO os_ver;
+  HMODULE h;
+
+  ZeroMemory (&os_ver, sizeof (OSVERSIONINFO));
+  os_ver.dwOSVersionInfoSize = sizeof (OSVERSIONINFO);
+  if (!GetVersionEx (&os_ver))
+    return 0;
+
+  if (os_ver.dwPlatformId == VER_PLATFORM_WIN32_WINDOWS)
+    {
+      h = LoadLibrary ("Unicows.dll");
+      if (!h)
+	{
+	  int button;
+
+	  button = MessageBox (NULL,
+			       "Emacs cannot load the UNICOWS.DLL library.\n"
+			       "This library is essential for using Emacs\n"
+			       "on this system.  You need to install it.\n\n"
+			       "However, you can still use Emacs by invoking\n"
+			       "it with the '-nw' command-line option.\n\n"
+			       "Emacs will exit when you click OK.",
+			       "Emacs cannot load UNICOWS.DLL",
+			       MB_ICONERROR | MB_TASKMODAL
+			       | MB_SETFOREGROUND | MB_OK);
+	  switch (button)
+	    {
+	      case IDOK:
+	      default:
+	        return 0;
+	    }
+	}
+      FreeLibrary (h);
+      return 1;
+    }
+  return 1;
+}