Positioner i Text fält

<tr>
  <td>Line 1:
  <input class="toolButton" type="button" value="b" onClick="line1.value=line1.value + '[b] [*b]'" />
  <input class="toolButton" type="button" value="u" onClick="line1.value=line1.value + '[u] [*u]'" style="font-weight:normal;text-decoration:underline;" />
<input class="toolButton" type="button" value="i" onClick="line1.value=line1.value + '[i] [*i]'" style="font-weight:normal;font-style:italic;" /><br>
<input type="text" size="47" name="line1" id="line1" value="Workshop" /></td></tr>

Detta lägger bara till sist i rade hur får jag den att lägga till mina taggar i den position som cursorn har?