TextBoxTemplate for formatted numeric input[
^]
Think this is what you are looking for, shouldn't be to hard to adapt the sample code if you aren't up to following the article's explanation.
But me finding it on the this site, using a superquick Google-search for "vb.net format input textbox", (was result no. 3), tells me you asked before searching for it. Please search the web or this site before asking. I don't mind but not all do like it when the questions section gets swamped with this type of questions.
good luck!
-frank