Hi Blynx

If you have a look at blog/code/BlogHolder.php function requireDefaultRecords() you will see the code that adds the 3 widgets automatically when you install the Blog module

         $widgetarea = new WidgetArea();
         $widgetarea->write();
         
         $blogholder->SideBarID = $widgetarea->ID;
         $blogholder->write();
         $blogholder->publish("Stage", "Live");
         
         $managementwidget = new BlogManagementWidget();
         $managementwidget->ParentID = $widgetarea->ID;
         $managementwidget->write();
         
         $tagcloudwidget = new TagCloudWidget();
         $tagcloudwidget->ParentID = $widgetarea->ID;
         $tagcloudwidget->write();
         
         $archivewidget = new ArchiveWidget();
         $archivewidget->ParentID = $widgetarea->ID;
         $archivewidget->write();
         
         $widgetarea->write();

So you should be able add widgets using this code providing you create a suitable object, in this case the object is $blogholder.
Never tried it but that's the theory...