It appears that Microsoft is going to offer Vista users some form of free upgrades to the Windows 7 operating system, depending on the time of their purchase. According to TechARP.com, a site that has accurately predicted the company's moves in the past, Microsoft will be working with PC makers to offer a free or inexpensive upgrade path for people who buy Vista machines after July 1st.
This has yet to be confirmed by Microsoft so as of right now this still has to be labeled as a rumor. Nevertheless, a similar program was initiated just before the XP - Vista transition looking to prevent a slowdown in sales during the months leading up to the new operating system release.
There are a handful of restrictions for the upgrade besides the purchase date, of course, such as that the Vista product can only be upgraded to the associated edition of Windows 7 (for example, Windows Vista Home Premium to Windows 7 Home Premium) and the language version also has to be the same. In addition, TechARP says that the program is optional, meaning that not all OEMs might participate.