I had an occasion to try to build a sample app that talked to an HID (Human Interface Device) USB device. I downloaded the latest WDK and attempted to build it with VS2008. I got an error stating that _In_out_ was undefined. This thread was the most helpful but was not specific enough to help me. I figured out a fix which I posted to that thread.
I simply renamed the file C:\WinDDK\6001.18001\inc\api\sal.h so that it would not be found, and the version provided by Visual Studio 2008, C:\Program Files\Microsoft Visual Studio 9.0\VC\include\sal.h, gets used.