Version: 1.3.1 Use IP.Board to manage your comments.
I would recommend installing the plugin from your WP Plugins menu. Do a search for "ipb" and it should come up. You can update easier in the future this way. If you prefer to install it manually, see the comments below.
You will need to edit the Base Url, Base Path, Member ID, and enter the IPB category # that corresponds to at least one WordPress category. The Base Url should lead to your forum's main front page. The Base Path should be the server path to the same location for your IPB root files. This will be the directory path to the directory where the initdata.php file is located. The Member ID should be a valid member ID from your IPB forum, with access to post HTML and access to post in the categories. Usually, you can enter 1 and it will post as your default admin user. Create any WordPress categories you need for the blog, and return to the IPB Comments submenu if needed. You'll notice a list of each WordPress category printed to the right of some empty input blocks. Enter the IPB category where you wish the new topics to be entered, whenever a WordPress post is made in the WP category shown directly to the right.