Add the following tag to the page you want the form to appear on.

<form action="/cgi-sys/guestbook.cgi" target=guestwindow>
<input type="hidden" name="user" value="demoacct">
<input type="hidden" name="action" value="addguest">
<input type="hidden" name="basehref" value="http://demoacct.com">
<input type="hidden" name="template" value="default">
Name: <input type="text" name="name"><br>
Email: <input type="text" name="email"><br>
Url: <input type="text" name="url"><br>
Comments: <textarea name="comments"></textarea><br>
<input type="submit" value="Sign Guestbook">
</form>