I just came to the same conclusion... "You have selected the feature: Send unlimited game invites to players - choose from over 250,000 Members which is only available to full members of Chessworld.net".
Strange that I didn't notice that last night. I guess I was overcome with anticipation.
Is it worth looking at any other sites? freechess.org might be worth a try. Although firewalls might play havoc with the telnet interface.
Q: How many runners does it take to organise a chess tournament?