In the July CTP of .NET 3.0 (formerly WinFX) the XPS print driver (MXDW) is included in the package. This may have been missed by a lot of people because, frankly we kind of forgot to tell everyone. So, if you are using Windows XP and have been wondering how to get a hold of the latest XPS print driver - just download the July CTP. But DANGER - you have to go to this link directly.
There is a bug in setup on the main link on the .NET 3.0 site that causes the print driver to not be installed. We will hopefully get it fixed. In the meantime go to the link above.