VS 2008 Making sure a specific character will be typed in a text box

Hi ! Let me ask you an interesting question . Is there any way to directly replace a character when typing it in a text box ? I tried using the Replace function which indeed replaces the character I want , but once it does it the cursor always moves at the beginning of the text box and practically makes the user start writing from the beginning instead of continuing the text he was typing . What I really want to replace the character in real time (maybe not even "replace" it but assure that a specific character will always be typed with another character) .
For example , I have a text box in which I want always the A character to be written as A . That is even if the user types a in a middle of word , it should always be typed A . Is there any way ?