BuddyPress.org

If you just want to display static content on the group’s home page in place of the activity stream, I wouldn’t go hacking activity-loop.php (it’s too far upstream, so to speak). In [your-theme]/groups/single/home.php, there’s a string of conditionals starting around line 28. Play with them to get what you want.

As for the current group id, you can get that from bp_get_group_id() when inside the bp_has_groups() loop.