Even though Nvidia would very much like to get into the netbook action, Intel is not making things easy for them. The recent introduction of its Ion platform, coupled with 9000 series mobile GPUs, has been pitched by Nvidia as a great way to expand the capabilities of Atom and make it more appealing to people who want a taste of performance along with better graphics support.
Intel will have none of that, however, with a recent internal statement revealing that the company will only be shipping the atom with their own chipsets, in particular their 945GSE and 945GC chipsets. They also have said through other channels that they have no intentions of testing or "validating" the MCP79 chipset for use with the Atom.
What are Intel's intentions with this move? There are clear advantages to joining with Nvidia in this endeavor. There's no question that Nvidia has a superior integrated GPU, and their chipsets are popular among enthusiasts. They have a proven track record of working with Intel CPUs as well, and a partnership might help keep Nvidia from making similar deals with AMD.
Perhaps Intel simply wants no other option than a pure-Intel offering, or does not want to erode the amount of money they are bringing in form the Atom. Nvidia is still working with other hardware manufacturers, trying to get them to support the Ion platform as well, hoping they will put pressure on Intel.