The company is promising that if you buy one of the games through Amazon via the links on their page, then they will send you for free their initial release of compatibility software that will let you"run these Windows Vista titles on Windows XP," they claim.
Said Falling Leaf Systems CEO Brian Thomason, "first [Microsoft] claim that it was impossible to implement DirectX 10 compatibility atop Windows XP, and now they also want us to believe that they couldn't successfully launch two DirectX 9 based titles on XP either. We plan to expose both theories as patently false."
We're not sure if the software will work as planned, or how Microsoft might try to prevent the games from going online. The expected shipment date is "within a few months," according to their press release; the pre-order page estimates late July.
[Via Xbox 360 Fanboy]
Microsoft Xbox One
Microsoft Xbox 360