Microsoft's Robbie Bach announced during their company's CES Keynote that a demo for Halo Wars will be available for download February 5th. Robbie has also announced that instead of Halo Wars being released March 3rd, they are now moving it to February 28th. Bach has also spoken about Halo 3 ODST still in the works and will in fact be out later this year, probably around October. More on the CES Keynote can be found
here.