If you have already run the install using the “buddypress out of the box” option, and need to get back to where you have options to install different theme support, just switch your theme temporarily to a theme that lacks buddypress support. It will then give you a message with the options to get buddypress themes (and clicking on that link in the message will take you to a plugin download page with the buddypress theme pack and other specific theme plugins you should install) OR the option to have buddypress help you modify your own theme, which will be a 3-step process in which buddypress will copy theme folders over to your theme folder, and then will give you instructions on how to modify the buddypress pages to match your theme.
