Before running NAnt that uses the P4Edit NAntContrib task ensure that you go into P4Win and from the menu select Settings | Use Current as Default.  Without doing this you may run into an error message that [some file] - must refer to client '[client name]'.

I have a version of NAntRunner working in Visual Studio 2005.  I was questioning whether there was a real need for NAntRunner in Visual Studio 2005 considering we now have MSBuild, but NAnt is just plain better and I've just gotten too used to running Ant builds from Eclipse.

Unfortunately the conversion from Visual Studio 2003 to 2005 is not exactly just a registry edit since you must recompile the plugin in Visual Studio 2005 to reference EnvDTE80 and remove the Office.dll dependency (see this MSDN article: http://msdn2.microsoft.com/en-us/library/ms165634(VS.80).aspx).  The one nice thing about VS 2005 is that the add-in facilities are easier to work with so I was able to eliminate several of the C++ based hosting projects/dlls.  It seems to work just fine, but I still need to get the configuration loading/saving working.  I also need to fix the installer project to reflect the xcopy based VS 2005 add-in deployment model.