Show up the On Screen keyboard if the user sets the focus on a textfield. WPF with .Net 4 Client profile

For my full screen WPF application, I need to show up the Windows 7 onscreen keyboard, if a user sets the focus on a textfield.

There's no hard keyboard for the panel, just a mouse device to interact with it. In this case I need a onscreen keyboard to fill up the textfields.

The WPF-application is written in C# .Net on the .Net Framework 4.0 Client profile.

Thanks for reply Andi