Ecco il codice.

codice:
<HTML><BODY>
<FORM name="ff" action="text.html" method="post">
<INPUT type="text" size="20" name="tb1" onBlur="restore();" onFocus="modify();" value="Inserire testo...">
</FORM>
<SCRIPT language="Javascript1.2">
<!--
function modify()
{
if (document.ff.tb1.value=="Inserire testo...")
{
document.ff.tb1.value="";
document.ff.tb1.click();
}
}

function restore()
{
if (document.ff.tb1.value=="")
	document.ff.tb1.value="Inserire testo...";
}
//-->
</SCRIPT></BODY></HTML>