Status bar

I don't think there is any specific widget for this, but like in a web browser I want to add a status bar to bottom of the window which has 100% width and can display text.

Would a simple TextBox control be best... I set up all my GUI using XML so how to programatically create this?

TextBox would be enough for status bar.
What about size - MyGUI doesn't support mixed sizes, so you need some additional code to stretch widget manually. Another common way is to make all gui layout one some fixed size invisible parent widget and always resize it to full size after load to make Aligns of child widgets do the trick.