From the declaration of expert Keith Leffler:
I have been asked by Plaintiffs' counsel to estimate the amount of revenue earned by Microsoft from the licensing of Windows XP on Vista Capable but not Vista Premium Ready PCs sold to Plaintiffs. In Microsoft's Supplemental Responses it estimates that it received revenue of [redacted] from Windows XP licenses on upgradeable PCs sold in the U.S. during the April 2006 through January 2007 period. From the estimates of Windows Capable but not Vista Premium Ready PCs compared to all upgradeable PCs as in Table 1, I estimate that [redacted] of the [redacted] from Windows XP licenses on upgradable PCs were for XP licenses on Vista Capable but not Vista Premium Ready PCs -- those PCs purchased by the Plaintiff class. From these figures, I have, therefore reached the opinion that Microsoft revenue from the Windows XP licensing on Vista Capable but not Vista Premium Ready PCs sold to Plaintiffs was $1.505 billion.
Dr. Keith Leffler is an economics professor at the University of Washington, his statement above was taken from part of his testimony on behalf of the plaintiffs in the ongoing class-action lawsuit that accuses Microsoft of deceiving consumers during its Vista Capable marketing program.
Source: Seattle PI - The Microsoft Blog