If you follow the instructions I gave above, you’ll have to edit the content of the screen by typing HTML directly into display() in the plugin. It’s a bit more complicated to make the pages editable by you on the front end.
The code on the codex page will actually function as a plugin, so that’s a good place to start. Instead of a stand-alone plugin, the easiest thing is to drop it inside of bp-custom.php (and if you don’t have a bp-custom.php already, create one in your plugins directory). Start playing around with the code to see what each part does.
You’ll need a separate class (the code on that page counts as a single class), with a different name, for each new tab.