One simple way is to use javascript.<p>Have your users add a single <script> tag in their html page, which points to a javascript file on <i>your</i> server.<p>That javascript file on your server is just a single statement:<p><pre><code> document.write(" ... [ widget content goes here ] ... ");
</code></pre>
which gets executed every time someone visits your user's site.<p>Just generate the javascript file on your server as often as necessary (and, obviously, you can have multiple javascript files customized for each of your users).