Well, there's a nice coincidence -- a brand-new (well, used, but not by me) M1400 and the Longhorn / Vista beta. In the words of the immortal James Doohan, “How do they mix? I'll let you know...”
Update: Microsoftian Hilton Locke warns “many of the user interface items (read: Tablet PC Input Panel, Journal, et al) are not in this release. We will be making an interim version of the Input Panel available for installation on Vista Beta 1, but I do not have final details on that just yet.”
Update: I chickened out. I need the M1400 to be fully functional for a project I'm starting on the 1st.