The textarea is not in the form therefore you will not be able to reference it from the form elements, just add it to the form.
<form name="form1">
<p>Girl's quaalities you want?</p>
<select name="listbox" onchange="tellMe(this.form)" multiple>
<option>Pretty</option>
<option>Sexy</option>
<option>Hot</option>
<option>Intelligent</option>
<option>Funny</option>
</select>
<br />
You Choose:<br />
<textarea rows="4" cols="20" name="textarea1"></textarea>
</form>