Just as how Microsoft gave late Windows Vista buyers an (almost) free upgrade path the Windows 7, it appears that the same will apply to those picking up Office 2007 in the months leading up to the release of Office 2010.
Ars Technica caught a cached copy of a bulletin posted on a Microsoft U.S. Partner Community website that specifies that customers who purchase and activate a copy of Office 2007, with or without a new PC, from an authorized reseller between March 5, 2010 and September 30, 2010 qualify for the promotion.
Those who satisfy the qualifications must request his or her free Office 2010 product by October 31, 2010 using an activated Office 2007 Product Key and a dated sales receipt.
Although this information is no longer available on the partner website, we suspect that the deal is real. Microsoft often makes these sort of "technology guarantees" and this information leak is likely just a case of the company revealing plans with its partners before making a formal announcement to the public. After all, letting this information out this soon could potentially halt all Office 2007 sales for the next month.
Here is the provided image regarding the free upgrade path: