display/hide textbox based on drop down list

Answer 1

<form name="form" action="" method="post">
<table>
<tr>
<td>
<select name="one" onchange="if (this.value=='yes'){this.form['yes'].style.visibility='visible'}else {this.form['yes'].style.visibility='hidden'};">
<option value="" selected="selected">Select...</option>
<option value="yes">yes</option>
<option value="no">no</option>
</select>
<input type="text" name="yes" style="visibility:hidden;"/>
</td>
</tr>
</table>
</form>