You can have multiple menus. You must initialize them one at a time, the same way you init a single menu; just make sure that the <UL>-s have different ID-s ;-)

As for the "fixed" stuff, there are several solutions:

1. [the most straightforward; doesn't work with IE].  Embed the top level menu in a DIV with style="position: fixed".  Then feel free to position that DIV anywhere you want.  Like this:

   <div style="position: fixed; left: 10px; top: 10px">
     <ul id="menu">
       ... the menu content
     </ul>
   </div>

   "position: fixed" is in the CSS specification for many long years now.  But, IE/Win does not support it.
   

2. Use an IFRAME for the page content.  The menu works pretty well with this in Gecko and Internet Explorer 5.5+, but fails on Opera, Konqueror, Apple Safari (browser bugs; they show the IFRAME on top of the menu).  However, the next version will contain a demo that shows this technique.

3. Use "position: fixed" for all browsers except Internet Explorer.  Work around Internet Explorer bugs by using a technique to emulate fixed position.

At Dynarch.com we are successfully using (3) for keeping the items on the left fixed.