Onlcik Add Another Table Row With Javascript.

i have no idea about javascript and have been fiddling with this form for a while now... i would love to be able to have a table containing a label in 1 column and a text box and buttun in the other.

When the button is clicked the javascript funcion adds another row to the table with another textbox and button to add more...

here's what i have so far..

Code:
<script language="Javascript">

function add_item() {
document.write ("<tr><td class='rachel'>Item Value</td><td><input name='listItems[]' size=&#3950;' type='text'><input type='button' value='Add More' onclick='add_item();'></td></tr>
");
}
</script>

This does what i want it to however, it opens in a new window instead of at the bottom of a table...