Customers looking to get their hands on Office 2010 when it comes out later on this year can do so, and for free. If customers purchase Office 2007 between March 5, 2010 and September 30, 2010, Microsoft will allow you to download and upgrade to Office 2010 for free.
However, Microsoft is only allowing certain software programs to be considered upgradable through your program including the following versions of Office 2007:
How exactly does the program work?
Customers who purchase Office Home and Student, Standard, Small Business, Professional or Publisher 2007 can upgrade to that a similar version of Office 2010 when released. Standard and Small Business editions will be upgraded to Home and Business & Professional edition.
Customers will be able to download - or order a DVD for a small fee - when Office 2010 is available to the public. Customers must also purchase one of the above versions of Office 2007 from an authorized dealer.
Consumers will still be eligible for a free upgrade with or without a new purchase of a PC, between March 5 and September 30th. Office 2007 sales and activations must take place during this time frame, in order to qualify for the free upgrade.
Source- Neowin