This entire thread is full of fail - a majority of the posts are uneducated guesses and make no sense.
In order to make a private server, you are going to go through a whole lot of trouble. If you want a good example, look at the source to MMO emulators like Mangos for WoW.
The client comes with XML data that actually gives you a lot more information than most MMOs would such as detailed object and monster data.
But take a few to think about what you don't have access to:
- Auth handler for accounts
- Connection handler for active player sessions
- AI/Pathing
- Loot drop tables / drop % rates
- etc, etc
You basically have to start with connecting a client to your own makeshift server to start figuring out the packet information the client sends and receives. It'd be a lot easier than spending a bunch of time de-obfuscating the entire SWF, but it still isn't -easy-. Even with all the packet information, you still have to code the entire server.
Someone already started something similar, but if you cannot do it yourself, you are not going to be able to finish it: -removed-
Not an easy undertaking whatsoever.