Nvidia released a GF 6600 reference model, that works at 350/800 with 256mb DDR2 modules. Other manufacturers have made DDR2 and DDR3 models but this one is a change in the reference, it seems all future 6600 will have at least DDR2. I recieved this info directly from Nvidia. It will be priced to compete with Radeon X1300Pro.

Quote Originally Posted by Nvidia PR Team
The GeForce 6600 DDR2 is the latest product introduction within the highly successful GeForce 6600 line. Now providing DDR2 instead of DDR for standard GeForce 6600 graphics cards, users can experience excellent mainstream 3D graphics performance at value segment pricing. We've been able to achieve faster core clocks as our manufacturing process has improved since 6600 initially launched. While XFX is obviously one of our key partners shipping a new DDR2 board, all of our major partners will be rolling out DDR2 skus in the very near future.

Clocked at 350MHz core and 400MHz memory (reference clocks) the GeForce 6600 DDR2 includes 8 pixel pipelines, 3 vertex shaders, and a 128-bit interface to its 256MB DDR2 frame buffer. Mainstream gaming and video playback has never been more powerful! Many current high-end 3D gaming titles will play comfortably at 1024x768 4xAA/8xAF, 1280x1024 4xAA/8xAF, or 1600x1200 1xAA/1xAF on a single GeForce 6600 DDR2 board. An SLI configuration will allow even better performance running current games with higher levels of image quality settings.

The NVIDIA GeForce 6600 GPUs deliver full support for all Microsoft® DirectX® Shader Model 3.0 (Microsoft DirectX® 9.0c) features including the Vertex Texture Fetch (VTF) capability missing from recently introduced competitive products. The 6600 GPUs also offer 64-bit floating point texture filtering for high dynamic-range (HDR) lighting effects, PureVideo capabilities enabled by on-chip video processors for high-quality digital media encoding and decoding, and mainstream SLI (Scalable Link Interface) dual-board graphics support.

Home theater PCs can benefit from PureVideo technology using a GeForce 6600 DDR2 board. PureVideo hardware and software provides superb picture clarity and precise, vivid colors across all high definition (HD) ATSC video formats. Powered by three separate video engines, the GeForce 6600 DDR2 delivers HDTV out (702p and 1080i), support for both 3:2 and 2:2 pulldown (inverse telecine), and spatial-temporal de-interlacing on HD content (with Release 80 drivers). PureVideo’s advanced scaling and deinterlacing technology allows DVD and other non-HD interlaced content to display incredibly clear, smooth, and artifact free video on progressive displays, ranging from PC screens to large screen HDTVs.

GeForce 6 DDR 2 boards are shipping now, so there is no embargo on this information.
I should be getting one of this made by XFX ASAP, I´ll let you know the numbers behind it. I´ve tested a Gigabyte 6600 and can overclock 80% in the GPU, let´s hope this one can do it even better