If you install software for an alternate input device, such as a slate or electronic whiteboard, Vista may helpfully decide that you are using a Tablet PC, and enable certain features that are irrelevant to the fact that you may just be using a normal desktop or laptop that doesn’t have the alternate device connected all the time.
I installed the Promethean Activboard software on my desktop, and since then, Vista gives me an onscreen keyboard at logon, and it also gave me the Tablet PC Input Panel, which sat on the edge of my desktop and got in the way whenever the mouse accidentally went over it.
Whilst I haven’t yet figured out how to get rid of the different logon screen, the Input Panel can be turned off in Control Panel –> Administrative Tools –> Services. Find the service named “Tablet PC Input Service”, stop the service and change its startup setting to Manual.