your thread subject asks about a list box and the body of your quesiton asks about a text box. you need to decide which one you want to know about because they are not the same. If you really want to know about a text box, then as Guile.NET has stated, it is trivial.

if you want to know about a list box, then (1) there is probably some way to do it through subclassing and/or API calls, but I don't know how, or (2) you can fake it by using a fixed width font such as courier and then putting a variable number of spaces onto the front of each item to make them all come out the same length