Since you have tagged it as VB.NET, I assume you are taking of Winforms.
Now, all you need is to tie a
OnKeyDown
event to the textbox. In code behind, at runtime, whenever a key is pressed, OnKeyDown method would be invoked. In it, check for the key stroke and accordingly decide if you want to allow it or not.
If needed, have a look at similar discussion
here[
^].