Also have the same problem with my local installation.
1) Installed WordPress: Worked
2) Got Buddypress as a plugin.
3) Got a message, that the .htaccess could not be changed due to missing permissions, so changed the permissions, then no error message appears
4) Choosed the Buddypress default theme
5) Choosed the permalink options
= I also get tese 404 error messages (for example /wordpress/activity/)
