Today, I downloaded BuddyPress ( http://www.buddypress.org ) and spent a good chunk of the day trying to apply it to my existing theme on this website. I wasn’t very successful, but I learned a lot about BuddyPress in the process. Then, I found a page in the instructions that I should have read first that explained how to install it in a secondary site so that it does not affect your primary site.
Ten minutes later, I had BuddyPress up and running with its default theme on my server here:
Feel free to register as a new user and take the system out for a spin, and be sure to kick the tires.