You can run as many Nuke sites from one database as space will allow, just edit the 2nd site's config.php exactly like the first one but change the value of $prefix and $user_prefix to something else like nuke2 for example, to create the new tables get nukesql.php, upload it to the new subfolder where the second config.php is and point your browser to it. Make a backup of your current database beforehand.