function getCheckboxes(table, rMin, rMax, cMin, cMax) {
	var checks;
	var r, c, i;
	for (r=(rMin==-1?0:rMin); r<=(rMax==-1?table.childNodes.length-1:rMax); r++) {
		for (c=(cMin==-1?0:cMin); c<=(cMax==-1?table.childNodes[r].childNodes.length-1:cMax); c++) {
			var inputs = table.childNodes[r].childNodes[c].getElementsByTagName("input");
			for (i=0; i<inputs.length; i++) {
				if (inputs[i].getAttribute("type").toLowerCase()=="checkbox") {
					checks.push(inputs[i]);
				}
			}
		}
	}
	return checks;
}

//row 1
getCheckboxes(document.getElementById("myTable"), 0, 0, -1, -1);
//row 1 - 2
getCheckboxes(document.getElementById("myTable"), 0, 1, -1, -1);
//row 1 - 2, col 3 - 4
getCheckboxes(document.getElementById("myTable"), 0, 1, 2, 3);
//col 3
getCheckboxes(document.getElementById("myTable"), -1, -1, 2, 2);