It took some mangling but I got it to work :)
I also changed the email_sfriend template to this, as it made more sense:
{htmldoctype}
<html>
<head>
<title>$bbtitle - tell a friend</title>
$headinclude
</head>
<body>
$header
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
<tr>
<td><img src="{imagesfolder}/vb_bullet.gif" align="middle" alt="vBulletin">
<normalfont><b> tell a friend</b></normalfont></td>
</tr>
</table>
<br>
<form action="vbsfriend.php" method="post">
<table cellpadding="{tableouterborderwidth}" cellspacing="0" border="0" bgcolor="{tablebordercolor}" {tableouterextra} width="{contenttablewidth}" align="center"><tr><td>
<table cellpadding="4" cellspacing="{tableinnerborderwidth}" border="0" {tableinnerextra} width="100%">
<tr>
<td bgcolor="{tableheadbgcolor}" colspan="2">
<p align="center"><normalfont color="{tableheadtextcolor}" class="thtcolor"><b>{tell a friend about us} </b></normalfont></p>
</td>
</tr>
$logincode
<tr>
<td bgcolor="{secondaltcolor}"><normalfont><b>Name Your Friend :</b></normalfont></td>
<td bgcolor="{secondaltcolor}"><normalfont><input type="text" class="bginput" name="sendtoname" size="25" maxlength="75"></normalfont></td>
</tr>
<tr>
<td bgcolor="{firstaltcolor}"><normalfont><b>E-mail Your Friend:</b></normalfont></td>
<td bgcolor="{firstaltcolor}"><normalfont><input type="text" class="bginput" name="sendtoemail" size="25" maxlength="100"></normalfont></td>
</tr>
<tr>
<td bgcolor="{secondaltcolor}"><normalfont><b>Subject:</b></normalfont></td>
<td bgcolor="{secondaltcolor}"><normalfont>
<input type="text" class="bginput" name="emailsubject" value="An invitation from $bbuserinfo[username]" size="25" maxlength="100">
</normalfont></td>
</tr>
<tr>
<td bgcolor="{firstaltcolor}" valign="top"><normalfont><b>Your Message:</b></normalfont></td>
<td bgcolor="{firstaltcolor}"><textarea name="emailmessage" rows="10" cols="50">Hey!
I've found $bbtitle ( $bburl/ ) and I love it! It's a great Lord of the Rings community with an amazing Image Gallery, come visit me!
See you there!
$bbuserinfo[username]</textarea></td>
</tr>
</table>
</td></tr></table>
<br>
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
<tr>
<td align="center"><normalfont>
<input type="submit" class="bginput" name="submit" value="Send" accesskey="s">
<input type="hidden" name="action" value="sendfriend">
</normalfont></td>
</tr>
</table>
$footer
</form>
</body>
</html>