Year, geocodezip's answer is correct. So change your code like this: (if you still in trouble, or maybe somebody else in the future)
<script type="text/javascript">
function initialize() {
var latlng = new google.maps.LatLng(-34.397, 150.644);
var myOptions = {
zoom: 8,
center: latlng,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById("map_canvas"),
myOptions);
}
google.maps.event.addDomListener(window, "load", initialize);
</script>