Say I have the following:
Given that you're responding to keydown events I assume that you want to make sure that the string behind the
TextBox adheres to the "60 chars per line" rule. If that's the case you should make an event that subscribes to the
TextChanged event on the
TextBox. There you can fix up the text and either truncate or break apart lines that are too long.
(edit) To solve the display portion you can do as Kafuka suggested: just make the box wide enough to hold 60 characters, and use a monospaced font if you want to be sure. If you've made sure the string is correct this should fall into line easily.