Is this possible?  I'd like to add a RangeValidator and a RequiredValidator to a text box, if this is possible can you provide an example of how to do so?  Thanks.

Yes of course.

You can use the ValidationGroup.

<font size="2">

 ValidationGroup group = new ValidationGroup(
                new ValidationItem(new AlnumValidator(false), txtUsername, TextBox.TextProperty),
                new ValidationItem(new NotEmptyValidator(), txtUsername, TextBox.TextProperty)
            );

Or simply use the Silverlight Forms Toolkit.

 formLogin.AddTextBox("username", "Username:", new IValidator[] { new NotEmptyValidator(), new AlnumValidator(false) });

http://silverlightvalidate.codeplex.com/Wiki/View.aspx?title=Examples

I tried to add that code to my control but it doesn't recognize ValidationGroup.  I looked online and it looks like this is in the System.Web.UI.WebControls namespace which does not appear to be available from the Add Reference menu in VS.  What am I overlooking here?  Thanks.

The ValidationGroup class exists in the exsportance.Silverlight.Validate namespace. Here is the class file in source control: http://silverlightvalidate.codeplex.com/sourcecontrol/changeset/view/19655?projectName=SilverlightValidate#169830

fascinating.  somehow i downloaded the controls from silverlightvalidator.codeplex.com, and then found this and didn't notice that this was silverlightvalidate.codeplex.com.  Very confusing, I wouldn't have guessed there would be two projects with such similar intent, but thanks for responding to my questions without treating me like a complete idiot :)