To install and use WM6.5 target you need to have VS2008 Pro or better (remeain in the VS2008 chain, no VS2010 or 2012); VS2008 SP1 installed; WM6 SDK installed and finally WM6.5 DTK (developer toolkit).
See also wm65 requirements at http://www.microsoft.com/en-us/download/details.aspx?id=5389
excerpt: - Microsoft .NET Compact Framework v2 SP2. - Important: "Visual C++ Smart Device Programmability", an option of Microsoft Visual Studio Setup, must be selected and installed during Visual Studio installation.