In particular we are developing for Intermec CK30/CK31 running Windows CE. We have an existing C++ project that also targets newer devices (running Windows Mobile 5/6).
The guy who has left this with us, just used to use both environments to develop the one set of source. But I would rather ditch one and develop for all in one environment.
You should be able to use VS2008 for all your development. You'll need to install the platform SDKs for the Intermec and WM versions (WM 4.2 and 5.0 standard should be there by default). VS2010 doesn't yet support Windows Mobile/CE development.