[squidsk]

You might not want to edit the default vbulletin files though in case they get changed. Just create a new file call cssrollup_myrollups and put the following content :

<?xml version="1.0" encoding="ISO-8859-1"?>
<css product="product_name_here">
  <rollup name="my-rollup.css">
    <template>sidebar.css</template>
    <template>widget.css</template>
    <template>tagcloud.css</template>
  </rollup>
</css>

This will create the rollup file, you'd then need to change the default behaviour for the rollup to be used instead of the individual css files. This would require a plugin that both removes the three css files in question and adds the rollup file.

EDIT: You can use existing rollup files if there's one that suits your needs, just use the name of the existing rollup file and the css will be added to it. Also don't forget you'll need to rebuild the styles for the changes to occur.