AMD says it is already shipping a low-end HD 3400 chipset with 40 stream (shader) processors and a mid-range HD 3600 sibling (120 stream processors) in notebooks as of today, beginning with ASUS' M50 gaming notebook [link to be active soon]. Future versions, such as a likely HD 3800 version, are also expected in the first half of 2008. Operating system support is not mentioned but may include Mac OS X as well as Windows XP and Vista.
You can find out more details about the latest Mobility series at electronista and also at AMD's website.
The ATI Mobility Radeon HD 3000 Series of discrete graphics allow you to experience the power of HD with graphics processing designed for how you work and play. Advance to the next generation of HD game performance and lifelike realism thanks to Microsoft DirectX 10.1 capabilities and PCI Express 2.0 support for fast throughput and superior overall system performance. Watch the latest Blu-ray and HD-DVD videos in full-HD 1080p image resolution off your graphics processor and reduce demands on your CPU. Enjoy breakthrough energy efficiency with superb performance-per-watt delivering exceptional battery life.