The first time we heard about a product from Nvidia called G100 was almost a year ago. This should be one of the codenames for the next generation Nvidia card, but it might not be the only one.
D8E is Geforce 9800GX2, and that is already a done deal, but after that comes a new high-end card. We know that this product is expected in the middle of this year and that Nvidia is working on it. The new codename is GT200 and we know that Dan Vivoli likes GT stuff, so we wouldn't be surprised that he came up with the name.
We can also tell you that this is one big chip, but no real surprises there.