jQuery.fn.alpha = function(callback)
{
	var callback = typeof callback == "function" ? callback : function(){};
	var allow=false;
	this.keypress(
		function(e)
		{
			var key = e.charCode ? e.charCode : e.keyCode ? e.keyCode : 0;
			// allow enter/return key (only when in an input box)					
			if(key == 13 && this.nodeName.toLowerCase() == "input")
			{
				return true;
			}
			else if(key == 13)
			{
				return false;
			}
			
			if(
				key == 8 /* backspace */ ||
					key == 9 /* tab */ ||
					key == 13 /* enter */ ||
					key == 35 /* end */ ||
					key == 36 /* home */ ||
					key == 37 /* left */ ||
					key == 39 /* right */
				)
			{
				 return true;
			}
			
			
			if (key<38 && key!=32) return false;
			if (key>39 && key<45) return false;
			if (key>46 && key<64) return false;
			if (key>90 && key<97) return false;
			if (key>122 && key<192) return false;
			
			return true;
		}
	);
	return this;
}