How to get this working on Linux/Apache:
Create a new directory /var/www/monitor and copy all files htdocs/* files there.
Include these lines in /etc/apache2/httpdocs
---
Options +ExecCGI
AddHandler cgi-script .cgi
---
Restart Apache: sudo /etc/init.d/apache2 restart
Check that the perl XML-RPC modules is available ("sudo apt-get install librcp-xml-perl" on Ubuntu)
Edit /var/www/monitor/monitor.cgi to update the IP addresses for the Grid server (TODO: improve this)
Start OpenSim in grid mode, use a browser to open http://localhost/monitor/monitor.cgi