2.6.3 As the ball is falling the server shall strike it so that it touches first his court and then, after passing over or around the net assembly, touches directly the receiver's court; in doubles, the ball shall touch successively the right half court of server and receiver.
The bolded text is the only extra requirement of the service rules for doubles play. This means that all the other rules for service still apply, with the extra requirement that the ball must touch the right half court of the server, then the right half court of the receiver.
This also means that technically it is legal for the server to serve around the net rather than over it, just as for singles. In practice, it is virtually impossible to achieve this feat, so I doubt there will ever be any cause for argument!
Video - Law 2.6.3 - 8MB, 640x480 pixels
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