BuddyPress.org

In which format is your user list ? And does that list contains the same # of columns (10) as wp_user table ?

If you have access to the DB and phpMyAdmin, you can do this directly with mySql.
phpMyAmin has an import/export tool.

Note that if the site is already pw-protected, importing only usernames and emails won’t let them access. You need also to import a pw for them.