var string = "Enter search terms"; 

function search()
{ 
if(document.form_search.keywords.value == "" || document.form_search.keywords.value == string)
{ document.form_search.keywords.value = string; }
else
{ location.href = 'index.php?id=search&keywords=' + document.form_search.keywords.value; }
}

function check_search()
{ 
if(document.form_search.keywords.value == string)
{ document.form_search.keywords.value = ""; }
}