if (document.images) {
	// ======================= preload rollover main navigation button images
	var nav_campaign_over = new Image (); nav_campaign_over.src = "/images/nav_01_campaign_over.gif";
	var nav_event_over = new Image (); nav_event_over.src = "/images/nav_02_event_over.gif";
	var nav_program_over = new Image (); nav_program_over.src = "/images/nav_03_program_over.gif";
	var nav_teacher_over = new Image (); nav_home_over.src = "/images/nav_04_teacher_over.gif";
	var nav_trial_over = new Image (); nav_home_over.src = "/images/nav_05_trial_over.gif";
	var header_hoiku_over = new Image (); header_hoiku_over.src = "/images/header_nav_08_hoiku_over.gif";
	var header_kaiga_over = new Image (); header_kaiga_over.src = "/images/header_nav_14_kaiga_over.gif";
	// ======================= preload rollover some common images
	var b_top_over = new Image (); b_top_over.src = "/images/b_top_over.gif";

	// ======================= preload rollover images for each page
	if (whichCategory == "home") {
		var promo1_02_over = new Image (); promo1_02_over.src = "/images/promo1_02_over.gif";
		var promo2_02_over = new Image (); promo2_02_over.src = "/images/promo2_02_over.gif";
		var promo3_02_over = new Image (); promo3_02_over.src = "/images/promo3_02_over.gif";
		var promo_pg_02_over = new Image (); promo_pg_02_over.src = "/images/promo_pg_02_over.gif";
	}
	if (whichCategory == "program") {
		// chart images
		var program_chart_04_over = new Image (); program_chart_04_over.src = "/images/program_chart_04_over.gif";
		var program_chart_13_over = new Image (); program_chart_13_over.src = "/images/program_chart_13_over.gif";
		var program_chart_08_over = new Image (); program_chart_08_over.src = "/images/program_chart_08_over.gif";
		var program_chart_10_over = new Image (); program_chart_10_over.src = "/images/program_chart_10_over.gif";
		var program_chart_16_over = new Image (); program_chart_16_over.src = "/images/program_chart_16_over.gif";
		var program_chart_18_over = new Image (); program_chart_18_over.src = "/images/program_chart_18_over.gif";
		// other images
		var b_trial_over = new Image (); b_trial_over.src = "/images/b_trial_over.gif";
	}
	if (whichCategory == "campaign") {
		// other images
		var b_enrol_tel_over = new Image (); b_enrol_tel_over.src = "/images/b_enrol_tel_over.gif";
	}
	if (whichCategory == "event") {
	}
	if (whichCategory == "teacher") {
	}
	if (whichCategory == "trial") {
	}
	if (whichCategory == "contact") {
	}
	if (whichCategory == "map") {
	}
	if (whichCategory == "hoiku") {
	}
	if (whichCategory == "kaiga") {
	}
	if (whichCategory == "pg") {
	}
}