Validation of WPF User Input using MVVM and Entity Framework 4.0 -

I am creating a WPF 4.0 application using MVVM. The model unit is generated using Framework 4.0. I am using data binding on WPF to bind user input for model input.

What is the easiest way to validate user input? I like an approach where I can set the verification rules on the model rather than WPF. How can this be done? Any sample is appreciated.