Estoy intentando enganchar, por ejemplo, el Bloc de notas sin éxito. Hacer un gancho global parece funcionar bien.

Pruebas en XP SP2.

Edit: el código modificado funciona ahora.

MyDLL code

#include <windows.h>
#include <iostream>
#include <stdio.h>

HINSTANCE hinst;
#pragma data_seg(".shared")
HHOOK hhk;
#pragma data_seg()
//#pragma comment(linker, "/SECTION:.shared,RWS") compiler error in VC++ 2008 express

LRESULT CALLBACK wireKeyboardProc(int code, WPARAM wParam,LPARAM lParam) {  
    if (code < 0) {
        return CallNextHookEx(0, code, wParam, lParam);
    }
    Beep(1000, 20);
    return CallNextHookEx(hhk, code, wParam, lParam);
}

extern "C" __declspec(dllexport) void install(unsigned long threadID) { 
    hhk = SetWindowsHookEx(WH_KEYBOARD, wireKeyboardProc, hinst, threadID);
}
extern "C" __declspec(dllexport) void uninstall() {
    UnhookWindowsHookEx(hhk); 
}

BOOL WINAPI DllMain(__in HINSTANCE hinstDLL, __in  DWORD fdwReason, __in  LPVOID lpvReserved) {
    hinst = hinstDLL;
    return TRUE;
}

Mi program

#include <Windows.h>

unsigned long GetTargetThreadIdFromWindow(char *className, char *windowName)
{
    HWND targetWnd;
    HANDLE hProcess;
    unsigned long processID = 0;

    targetWnd = FindWindow(className, windowName);
    return GetWindowThreadProcessId(targetWnd, &processID);
} 

int _tmain(int argc, _TCHAR* argv[]) {
    unsigned long threadID = GetTargetProcessIdFromWindow("Notepad", "Untitled - Notepad");
    printf("TID: %i", threadID);    

    HINSTANCE hinst = LoadLibrary(_T("MyDLL.dll")); 

    if (hinst) {
        typedef void (*Install)(unsigned long);
        typedef void (*Uninstall)();

        Install install = (Install) GetProcAddress(hinst, "install");
        Uninstall uninstall = (Uninstall) GetProcAddress(hinst, "uninstall");

        install(threadID);

        Sleep(20000);

        uninstall();
    }

    return 0;
}