#include <windows.h>

int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
MessageBox(NULL, "Простейшая программа!","WinAPI App", 0); //сообщение
return 0;
}

1.cpp
c:\documents and settings\********\мои документы\visual studio 2008\projects\w\w\1.cpp(8) : error C2664: 'MessageBoxW' : cannot convert parameter 2 from 'const char [22]' to 'LPCWSTR'
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
Build log was saved at "file://c:\Documents and Settings\********\Мои документы\Visual Studio 2008\Projects\w\w\Debug\BuildLog.htm"
w - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========