Widgetizing a side bar and allowing for certain outside plugins?

Before widgets came onto the scene, I had gotten into the habit of putting provisional code into my sidebar to run a certain plugin if it existed and to ignore it if it did not. Here is an example:

<!-- YEARS PAST ARCHIVES -->
<?php if (function_exists('showYearsAgo')) { ?>
<li id="yearsago"><h2>Daze Gone By</h2>
<ul>
<?php showYearsAgo(3,'<li>','</li>',true,'.'); ?>
</ul>
</li>
<?php } ?>


Is this kind of coding still necessary when developing themes and if so, how can it be implemented in the sidebar that has the widgetizing code in it? In other words, I just need to know where to put this code.

Thanks!