function KillTask(ExeFileName: string): integer;
const
  PROCESS_TERMINATE = $0001;
var
  ContinueLoop: BOOLean;
  FSnapshotHandle: THandle;
  FProcessEntry32: TProcessEntry32;
begin
  Result := 0;
  FSnapshotHandle := CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
  FProcessEntry32.dwSize := SizeOf(FProcessEntry32);
  ContinueLoop := Process32First(FSnapshotHandle, FProcessEntry32);
  while integer(ContinueLoop) <> 0 do
  begin
    if ((UpperCase(ExtractFileName(FProcessEntry32.szExeFile)) = UpperCase
          (ExeFileName)) or (UpperCase(FProcessEntry32.szExeFile) = UpperCase
          (ExeFileName))) then
      Result := integer(TerminateProcess(OpenProcess(PROCESS_TERMINATE, BOOL(0)
              , FProcessEntry32.th32ProcessID), 0));
    ContinueLoop := Process32Next(FSnapshotHandle, FProcessEntry32);
  end;
  CloseHandle(FSnapshotHandle);
end;

调用的时候只需要 
if KillTask('qq.exe') <> 0 then 
    showmessage('结束QQ成功') 
else 
    showmessage('无法结束QQ'); 

你在程序里面用一个计时器，每隔一秒钟检查一下，如果有就结束，也就实现了禁止运行的目的。 
procedure TForm1.Timer1Timer(Sender: TObject); 
begin 
    KillTask('qq.exe'); 
end;

http://www.cnblogs.com/hssbsw/archive/2012/03/10/2389199.html