document.onkeydown = NavigateThrough;

function NavigateThrough (event)
{
	if (!document.getElementById) return;

	if (window.event) event = window.event;

	if (event.ctrlKey)
	{
		code = event.keyCode ? event.keyCode : event.which ? event.which : null;
		if (code) {
			key = String.fromCharCode(code).toLowerCase();
		}

		switch (key)
		{
			case "c":
			case "x":
			case "a":
				event.returnValue=0;
				break;
		}

	}			
}