<SCRIPT LANGUAGE="JavaScript">   
currentTime = new Date();   
if (currentTime.getHours() >= 6 && currentTime.getHours() <= 11 )   
document.write("Доброе утро, ");   
if (currentTime.getHours() >= 12 && currentTime.getHours() <= 17 )   
document.write("Добрый день, ");   
if (currentTime.getHours() >= 18 && currentTime.getHours() <= 23)   
document.write("Добрый вечер, ");   
if (currentTime.getHours() >= 0 && currentTime.getHours() <= 5)   
document.write("Доброй ночи, ");   
</SCRIPT>