how to add tags into an input field?

i have no idea about js, so guess thats an easy one:
on my form is a textarea "tags" and some links below. now i want this linktext in my formfield if someone clicks on it - as seen on del.icio.us on this "submit a site " page. so here is what i got so far:

function addtag(tagname) {
	document.submitform.tags.value = document.submitform.tags.value + tagname;
}	

Code (markup):

<form action="submit.php" method="POST" id="submitform">
			<table style="width:100%">
			<tr>
			<td>URL:</td><td><input type="text" name="url" value="" size="60"></td>
			</tr>
			<tr>

			<td>Tags:</td><td><input type="text" id="tags" name="tags" size="60"><br>
			Common Tags: <a href="javascript:addtag('Free')">Free</a>, <a href="javascript:addtag('Paid')">Paid</a>, <a href="javascript:addtag('Recip')">Recip</a>
			</td>
			</tr>

HTML:

any ideas....?

 

change your line to this:

document.forms['submitform'].tags.value = document.forms['submitform'].tags.value + tagname;

Code (markup):