You Can Get There from Here, Part 1

I need help with Squirrelmail. Basically, I am trying to add my own logo to the top-left bar. I don't know much about programming, but I installed the setup.php file for the plugin under:

../plugins/addgraphic/setup.php

I made sure to direct the links within the setup.php to my new graphic under:

../images/posvarmail.jpg

Finally, I tried adding

$plugins[0] = 'addgraphic';

to the config.php file. But where do I add it? Anywhere? I just put it at the end. The other option is to simply "execute" the configure script. But how the heck do I "execute" a script? Do i need some sort of special software for that? All I am using is the domain manager screens. And I have no "execute" option, only edit or delete options.

Any help would be greatly appreciated.

Thanks!

Jeremy P.