to start developing for a Mobile Internet Device I would recommend you have a close look at http://www.moblin.org and register in the community there. For multimedia player codecs and the like I would recommend you have a look at http://www.helixcommunity.org. There you can get access to the repository for the entire helix media player software stack.

As far as a development platform to use, I would simply do a search for Mobile Internet Devices or netbooks on the web. It may be easier to start developing for a Intel Atom based netbook ideally running Linux, but you can also install a standard Linux or Moblin compliant Linux* on a netbook afterwards..

Intel's development tools supporting Moblin and Mobile Internet Devices are available at http://www.intel.com/software/products/mid/

Thanks.