Microsoft has releases a preview of Internet Explorer 9 at its MIX conference. They did not say it explicitly, but by now it is pretty clear that its new browser will not be supported in Windows Xp.
This is what Internet Explorer general manager Dean Hachamovitch said:
Building a modern browser requires a modern operating system.
Windows Xp is nearly a decade old and cannot be counted as a modern browser in any case. Moreover, IE9 will rely on hardware acceleration due to its use of Direct2D and DirectWrite technologies -none of which are available in Windows Xp.