It's confirmed. The news we heard last month has been confirmed by James Cameron himself, Sigourney Weaver is set to star in his next film Avatar.

The report comes from AICN who talked with Cameron just the other night, and is carried through Cinema Blend.

Cameron was also kind enough to point out some other confirmations for the cast:

Sam Worthington and Zoe Saldana...WES STUDI, SIGOURNEY WEAVER (confirmed as Grace), Peter Mensah, Joel David Moore...C.C.H. Pounder...

There's quite a bit more information on the techincals of what Cameron is doing, for instance his new motion capture system is real time rendering, making it much more director friendly. What that seems to mean is that they can capture the performance, run it through the system and see it live on screen, rather than with motion capture to date, run it through a team for months before seeing it.

Interestingly the call to AICN took place just as Cameron was returning from having shot three days of live action in the tropical rainforests of Kauai.