function check_username(username){
		b = true;
		if (username == ""){
			b = false;
			alert("Bitte geben Sie einen Benutzernamen ein.");
		}
		else if (username.search(" ") != -1){
			b = false;
			alert("Im Benutzername sind keine Leerzeichen erlaubt.");
		}
		else{
			var r = new RegExp("[^0-9A-Za-z]", "i");
			if (r.exec(username)){
				b = false;
				alert("Der Benutzername enthält unerlaubte Zeichen.");
			}
			else if (username.length > 12){
				b = false;
				alert("Der Benutzername ist zu lang. (max. 12 Zeichen)");
			}
		}
		return b;
	}
	
	function ImgPreload() {
		document.Vorladen = new Array();
		
		if(document.images) {
			for(var i = 0; i < ImgPreload.arguments.length; i++) {
				document.Vorladen[i] = new Image();
				document.Vorladen[i].src = ImgPreload.arguments[i];
			}
		}
	}

	function emailCheck (emailStr) {
		var emailPat=/^(.+)@(.+)$/
		var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
		var validChars="\[^\\s" + specialChars + "\]"
		var quotedUser="(\"[^\"]*\")"
		var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
		var atom=validChars + '+'
		var word="(" + atom + "|" + quotedUser + ")"
		var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
		var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")
		var matchArray=emailStr.match(emailPat)
		if (matchArray==null) {
			//alert("Ungültige Email-Adresse")
			return false
		}
		var user=matchArray[1]
		var domain=matchArray[2]
		
		if (user.match(userPat)==null) {
				return false
		}
		
		var IPArray=domain.match(ipDomainPat)
		if (IPArray!=null) {
			for (var i=1;i<=4;i++) {
				if (IPArray[i]>255) {
					alert("Ungültige Email-Adresse")
					//alert("Destination IP address is invalid!")
					return false
				}
			}
			return true
		}
		
		var domainArray=domain.match(domainPat)
		if (domainArray==null) {
			//alert("The domain name doesn't seem to be valid.")
			return false
		}
		var atomPat=new RegExp(atom,"g")
		var domArr=domain.match(atomPat)
		var len=domArr.length
		if (domArr[domArr.length-1].length<2 || 
				domArr[domArr.length-1].length>3) {
			 //alert("The address must end in a three-letter domain, or two letter country.")
			 return false
		}
		
		if (len<2) {
			var errStr="This address is missing a hostname!"
			//alert(errStr)
			return false
		}
		return true;
	}