Jon you talking about the offline missions?
Because if you are, that is part of the problem with the whole AI mission thing.
Its my understanding that HT hasn't figured out how to do it.
H2H the way it was is dead, and will stay dead.
User configurable arena's are in the process and should be released in the near future.
You will have to be a subscriber, you will go through the HTC password server. IE only subscribers will see them.
And they will be hosted on HTC's side not on your end.