function slideshow(book_id,offset){	
	// slide the handle 
	new Effect.Move('slideshow_handle', {x:offset, y:0, mode:'absolute', duration:0.3});
	// now hide the current visible book
	$$('div.slide_active').each(function(s){
		if(s.id != 'book_'+book_id){
			new Effect.Fade(s, {from:1, to:0, duration:0.5});
			s.removeClassName('slide_active')
		}
	})
	// show the selected book
	if(!$('book_'+book_id).visible()){
		new Effect.Appear('book_'+book_id, {from:0, to:1, duration:0.5});
		// add the active class
		$('book_'+book_id).addClassName('slide_active')
	}
}