Silverlight Validation & Tooltip Styles…
Silverlight 3 comes with built-in validation for many of the input controls. Setting them up is fairly easy and they are styled well enough that you could use them right out of the box.
If you would like to know how to set it up and also would like to customize the look and feel of the fields and validation message, this short tutorial will explain how to do just that.
Silverlight Validation