Installing new themes is a fairly simple process:
Download your chosen theme. For SlayerCafe, we are using the facebuddy theme.
Extract the ZIP file and upload it to the
/wp-content/bp-themes
folder.Enable the theme in the BuddyPress settings section of your WordPress MU control panel.
Your new theme should be visible on the BuddyPress-powered pages of your site.
You may have noticed that the process for installing a theme is very similar to the way WordPress MU handles themes. However, in the case of BuddyPress, you are setting the theme globally for your users.
If you would like to have the BuddyPress theme appear as the theme for your home page, you need to move the bphome theme from /wp-content/bp-themes/bphome
to /wp-content/themes/bphome
and enable it the way you would enable a normal WordPress MU theme.