Microsoft first shipped the XInput API in the October 2005 SDK. However the only managed APIs for it are included in the Managed DirectX for .Net 2.0 beta assemblies which are not always convenient to use. So until that code reaches RTM there are several managed wrappers around the native DLL that you can use from .Net 1.1 (or 2.0 if you just want to avoid the beta code).

• MDXInfo has a simple XInput wrapper library
• Brains'n'brawn has /mceXInput
• Don Box also has wrote a wrapper for an MSDN video

I'm pretty sure I've seen a couple more too, if you know of any other wrappers then email them to me.

See also When to use XInput and XInput/Direct Input detection code