For testing reasons, I set this during my htacces:

order deny, allow
deny from all
allow from 123.456.789.000

But Opera shows:

Internal Server Error The server
experienced an interior error or misconfiguration and was not able to complete your request.

Error log shows:

[Thu February 24 04:05:12 2011] [alert] [client 123.456.789.000] /var/www/vhosts/ order takes one argument, 'allow,deny', 'deny,allow', or 'mutual-failure'

Exactly what does this suggest? What shall we be held doing wrong? Thank you for helping with this particular.

You've got a space inside your Order directive argument.