There's a bit more to this than you may think as you'll need to allow navigation and edit key combinations in your text box so just dropping the characters you don't want isn't enough. Also, you'll need to handle pasting of information to make sure it's valid. I wrote an article[^] that does something similar - only numbers - but it can easily be adapted. It doesn't handle text that may be placed programatically, but a little checking in OnTextChanged would handle that.
Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)