var search_text   = 'ここから商品を検索できます';
var onfocus_color = '#000';
var onblur_color  = '#999';

if (document.searchbox.getAttribute("style")
    == document.searchbox.style) {
    // IE
    document.searchbox.setAttribute("onsubmit", 
        new Function("return onsubmitSearchbox()"));
} else {
    // other
    document.searchbox.setAttribute("onsubmit", "return onsubmitSearchbox()");
}

var search_box = document.searchbox.word;
search_box.value = search_text;
search_box.style.color = onblur_color;

function onfocusSearchbox() {
    if (search_box.value == search_text) {
        search_box.value = '';
        search_box.style.color = onfocus_color;
    }
}

function onblurSearchbox() {
    if (search_box.value == '') {
        search_box.value = search_text;
        search_box.style.color = onblur_color;
    }
}

function onsubmitSearchbox() {
    if (search_box.value == search_text || search_box.value == '') {
        return false;
    }
    return true;
}