Autodesk released a reduced-function edition of Inventor last year in preview mode. The plan was to decide what to do with the product this time this year. They've decided to keep it free (for at least another year), as well as update some of its features to match Inventor 2009 in some ways.
Inventor LT Technology Preview 2009 will become available before the current one expires May 1, 2008; it'll be free, but will stop working roughly a year later. (It's not yet available.)