Silverlight MVVM Validation

Input Validation – UI Exceptions & Model Validation Errors « Karl On WPF – .Net

http://karlshifflett.wordpress.com/mvvm/input-validation-ui-exceptions-model-validation-errors/

Using a ViewModel to Provide Meaningful Validation Error Messages « Josh Smith on WPF

http://joshsmithonwpf.wordpress.com/2008/11/14/using-a-viewmodel-to-provide-meaningful-validation-error-messages/

Silverlight, Validation and MVVM - Part II

http://www.thejoyofcode.com/Silverlight_Validation_and_MVVM_Part_II.aspx