First off, skip writing a new engine, just use an existing one. It makes it much easier, and reduces the problems you'll run into.
There are plenty of engines out there which you can either use freely, or buy a license for. (Some allow you to start using for free until you charge for the game, then you have to pay).
Two, find some good network programmers! You'll need a server which can support
many connections, and it needs to be very stable (or easily switch to a backup server.
The system should support streaming updates to the client whilst the player is in the game, so that your players won't need to download patches separately.
You'll need to come up with a protocol that can handle packet loss, and won't require too much data being sent back and forth.
There is what appears to be a pretty good wiki article about building your own MMORPG
here which I think you should read...
Then there is a project which'll simplify building an MMORPG which you can find
here. It's not out yet, but I'm sure you can use the time developing the assets for the game.
I don't have any time to help you develop the game, as I've got three university projects that require all my attention (develop a game for Xbox 360 using XNA, learn how to code HLSL Shaders and then an easy one which is just to create a game with
Game Maker). But you might find more people interested if you describe the project a bit more. If someone is going to dedicate their spare time to a project, it has to be with something they find interesting, and it's easier to decided that if you tell them something about the world..
Also, you might want to check out
Top Secret which is a new online game by Acclaim where you can help come up with ideas for it. And if you contribute a lot, and are lucky, you'll get a chance to develop an MMO with a profesional team!
Good Luck!
