[kh99]

If you can find the code for a "php direct execution" cms widget, I believe in many cases you can use that code directly in a "custom html/php" forum block. One minor difference is that php code for a widget assigns it's html to a $output variable while a forum block needs to return the html as a string, but you should be able to take cms widget code and add "return $output;" as the last line and achieve the same thing.

There may be other problems with accessing variables like $vbulletin, but they should be easy to fix.