e.g.
Main Index
--Sidebar
--Archive Widgets Group

Is that what is not working? Is the sidebar for the Main Index Page, or some other template like Entry?

On my Main Page, I have a hyperlinked Category Title, and the link is to that Category Archive page, followed by 2 entries for that category. It's not very elegant as I place the actual category name in the title. But, perhaps this will steer you in the right direction to what you want to do.

                    <div class="module-content">     
                     <div class="module-title"><a href="http://www.voidnow.org/antiincumbent_news/">Anti-Incumbent News</a></div>
                     <MTEntries category="Anti-incumbent News" lastn="2">
                      <$MTEntryTrackbackData$>

                      <MTDateHeader><h4 class="date-header"><$MTEntryDate format="%x"$></h4></MTDateHeader>

                      <a id="a<$MTEntryID pad="1"$>"></a>

                      <div class="entry" id="entry-<$MTEntryID$>">

                       <h3 class="entry-header"><$MTEntryTitle$></h3>

                       <div class="blue-entry-content">

                        <div class="entry-body">

                         <$MTEntryBody$>