Re: Serious Server Issues…
From the source of install.php:
// Let's check to make sure bb isn't already installed.
...
if ( $installed )
...
die(__('<h1>Already Installed</h1><p>You appear to have already installed bbPress. Perhaps you meant to run the upgrade scripts instead? To reinstall please clear your old database tables first.</p>') . '</body></html>');
I think it would just work by browsing to your forum in that case.