+3  A: 

You'll want to use a RichTextBox for that.

HTH, Kent

Kent Boogaart
+3  A: 

Like Kent said with a TextBox you're stuck with one color.

Here is a small article on simple RTB syntax highlighting that should give you most of what you need.

http://blogs.microsoft.co.il/blogs/tamir/archive/2006/12/14/RichTextBox-syntax-highlighting.aspx

Andrew Barrett