Re: Windows Server 2008 IIS7
I assume there’s nothing useful in your server’s log files? 500 is usually a misconfiguration of some type. Have you tried to upload a copy of the BuddyPress files rather than the automatic download?
Also, fyi, https://codex.buddypress.org/developer-docs/iis7-web-config/ which may be of some help once you get the plugin activated