Ok, i've been toying around with Visual Studio 2005, the In The Hand bluetooth API and Windows Mobile Pocket PC SDK and the .NET Compact Framework.  Here's what I got working;

Basing my code on the chat app which came with the v2.0.60828 InTheHand API, I've got a Windows Mobile 5.0 device application running on my T-Mobile MDA Vario and a Windows application running on XP.  The Windows app uses the DLL found in the \Assemblies\XP2 directory and the mobile app uses the \Assemblies\CE2 directory.

Without the need for pairing, I've got the device sending key inputs to the windows application, which can then display these or transfer the via the WinForms API to windows in order to control XP.

This pair of apps is not yet complete, but is showing very promising results.  Just thought I'd share what I've found.

Matt.