Re: to install in my hosting wordpress.org BuddyPress, required wordpress.com account
== required wordpress.com account for this to WordPress.org? ==
No, WP.com account is not required to install WordPress. You should know this as I’ve seen some of your posts at WP.org
=== multi-users functionality of WordPress 3.1 is similar to multi-blogs(multi-sites)? ===
Not exactly. A single WP site can have multiple users. When you https://codex.wordpress.org/Create_A_Network, you can create many sites with one WP installation. [edit] And each site in the network can have a single user or multiple users, it all depends on the set up.
For more information, post in Multisite forum at WP.org – https://wordpress.org/support/topic/welcome-to-the-multisite-forum?replies=2
Good luck.