[rolph]

А если несколько блоков? Надо через switch?

function doBlock(id) {
switch (id) {
	case first:
	{
	  document.getElementById(id).style.display = "block";
	  document.getElementById('second').style.display = "none";
	  document.getElementById('third').style.display = "none";
	  document.getElementById('fourth').style.display = "none";
	}
	case second:
	{ 
	 document.getElementById(id).style.display = "block";
	  document.getElementById('first').style.display = "none";
	  document.getElementById('third').style.display = "none";
	  document.getElementById('fourth').style.display = "none";
	}
	case third:
	{ 
	 document.getElementById(id).style.display = "block";
	  document.getElementById('first').style.display = "none";
	  document.getElementById('second').style.display = "none";
	  document.getElementById('fourth').style.display = "none";
	}
	case third:
	{ 
	 document.getElementById(id).style.display = "block";
	  document.getElementById('first').style.display = "none";
	  document.getElementById('second').style.display = "none";
	  document.getElementById('fourth').style.display = "none";
	}	
	} 
}