Well if you don't know, then why did you reply? You'd be better off keeping your mouth shut.
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To answer your question, wilhelmae, if it is illegal in any form then its still illegal. Since you'd be advertising an act that would cross state and country lines, that would also make it illegal (against their Acceptable Use Policy)
However, hosting online servers that accept money, not necessarily gambling, isn't illegal in the United States (because if it is, then we have a HUGE problem) so I'd contact ThePlanet's Legal department and ask specificaly what you would be advertising for and let thier lawyers look at the fine print.
Legal Department's email : legal-response@theplanet.com
Or refer to a contact on this page
http://www.theplanet.com/contact.html