Well, there is Domtab which it looks like he’s using to have the tabs. For the actual list of popular posts he’s probably using something like the Popularity Contest plugin.
Simply create a file called single.php with the contents of your current index.php file. Then add whatever customizations you want to the single.php file. The changes should be reflected across all your single blog post pages.
Well this sure is a pain…I guess I’ll have to use Flexible Upload on a 2.3 blog and transfer the images over to my 2.5 blog. An update would be greatly appreciated. ??