[Jerry]

You can set up the rest as you wish, if the link isn't found it defaults to the standard 404 file, if you want to parse the content to find if it's old forum or not before the script that's just another way of doing it, you can .htaccess and only direct old forum links to it if you want, that would lower the dB load onto the webserver.

This script is just an example and works for most, though not the only and de facto way of doing it.

The resulting 301 will update the search engines over time as it is.