checate este codigo. Son 2 funciones para agregar una linea (con select y 2 input) y borrar la ultima linea
Código:
<html>
<head>
<script>
var contLin = 3;
function agregar() {
var tr, td;
tr = document.all.tabla.insertRow();
td = tr.insertCell();
td.innerHTML = "<select id='sel" + contLin + "'>" +
"<option>1" +
"<option>2" +
"<option>3";
td = tr.insertCell();
td.innerHTML = "<input type='text' id='t" + contLin + "1' value='t" + contLin + "1'>";
td = tr.insertCell();
td.innerHTML = "<input type='text' id='t" + contLin + "2' value='t" + contLin + "2'>";
contLin++;
}
function borrarUltima() {
ultima = document.all.tabla.rows.length - 1;
document.all.tabla.deleteRow(ultima);
contLin--;
}
</script>
</head>
<body>
<table id="tabla" border=1>
<tr>
<td><select id="sel1">
<option>1
<option>2
<option>3
</td>
<td><input type="text" id="t11" value="t11"></td>
<td><input type="text" id="t12" value="t12"></td>
</tr>
<tr>
<td><select id="sel2">
<option>1
<option>2
<option>3
</td>
<td><input type="text" id="t21" value="t21"></td>
<td><input type="text" id="t22" value="t22"></td>
</tr>
</table>
<br>
<input type="button" value="Agregar" onclick="agregar()">
<input type="button" value="Borrar ultima" onclick="borrarUltima()">
</body>
</html>