The device manufacturer should be able to build that into the OS for you
(it's in Platform Builder). Citrix has one, of course. I'm not sure that
there's a download from MS, though.
If you have an iPaq 5000 series - its already installed in the ROM. If you
have another device - it will more than likely be on the support CD shipped
with your device. If you can't find it - you can download it fro ZDNET: http://downloads-zdnet.com.com/3000-2178-10179939.html