Changing the TextBox fonts

Question

Hi,
I have a textbox into which text is written programatically.
As I have a structured text format, I want to change programatically to fixed size characters, like Curier .
I found out that TextBox (as well as RichTextBox) have numerous properties like FontFamily and FontName, but they are all read only.
As font is a standard TexBox property, there must be a way to change it programatically????????
Thaks,
Sam