To back up an old vBulletin forum without admin access, consider the following approach: First, scrape the forum using tools like HTTrack or SiteSucker to create a local copy of the site. For data preservation and migration, look for known vulnerabilities in the vBulletin version to potentially access the database (metasploit can be a resource). Ensure any data extracted is handled ethically, respecting user privacy and legal considerations.