function openvensterpopup(url, breed, hoog, Name){
	screenx = screen.availWidth;
	screeny = screen.availHeight;

	breedte = breed;
	hoogte = hoog;

	toppos = (screenx - hoogte) / 2;
	leftpos = (screeny - breedte) / 2;

	venster = window.open(url, Name,'width='+breedte+',height='+hoogte+',screenx='+leftpos+',scrollbars=auto,status=1,screeny='+toppos);
	venster.focus();
}