Well I am looking for a way to use a CGI script on a Invision or PHPBB

To run a CGI script on the bulletin board itself, you'll need admin-level access to the server that the bulletin board is hosted on. I'm guessing if you had that, you wouldn't be asking the question, so the answer is probably "you can't do that".

However, what you probably can do is set up the script elsewhere and just link to it, the same way you'd link to any other offsite image. Assuming the bulletin board will let you link in an offsite image, all you need is an account with CGI priveges on any web server.

That's the best I can do without further details about what you want to do. I've never heard of Invision or PHPBB before.