How to make use of RegularExpressi onValidators in case of Windows Forms ?

[Intro]

I am currently using a Windows Application whcih contains many forms.
OIn one of the forms, I want to validate :

1.A TextBox(which will only accept digits 0-9)(the user won't be able top type any other except digits

2. Another textbox which will accept only [a-z} and [A-Z ], No other key will be allowed to be types in the textbox.

For the first requirement I used

System.Text.RegularExpressions.Regex myRegEx = new System.Text.RegularExpressions.Regex("^?{10}$");
if (myRegEx.IsMatch(txtBox.text)) {
    //  Is ok
}
else {
    //  Is not ok
}

But unfurtunately this didn't work for me.
kindly suggest a smarter way to validate.
Your answers would be appreciated.

Thanks in advance.