var current = 0;

function initArray() {

this.length = initArray.arguments.length;
  for (var i = 0; i < this.length; i++) {
  this[i] = initArray.arguments[i];
  }
}

var picz = new initArray(
"../images/stadium/stadium.jpg",
"../images/stadium/clubhouse.jpg",
"../images/stadium/gaststaette.jpg",
"../images/stadium/vip_lounge.jpg",
"../images/stadium/vip_lounge_view.jpg"
);


document.write('<img name="jscriptimg" src="'+picz[0]+'">');

function checkIt(val) {

var goodnum = current+val;

if (goodnum < 0) alert("Anfang der Bildergalerie!");
else if (goodnum > picz.length-1) alert("Ende der Bildergalerie!");
else document.jscriptimg.src = picz[goodnum];

current = goodnum;
}