Thanks for the quick answers!

I must apologize, because I still have problems with the language and I didn't explain myself properly.
What I want is to show an image in a fixed position; overlapping the message box, but not linked to the text, so the icon command doesn't work for me.
I want the image to be any size I want and in any position I want, just like in those games that show the face of the character inside of the textbox and not outside of it.
Edit (Nov-6-2012): well, seeing that there is no answer, I'll edit with the 'solution' I've found, just in case somebody has the same problem as me. Instead of displaying the textbox, I temporarily disable the textbox and display a static image that looks exactly like it. This way I can add images on top, because the textbox is actually an image like any other. It's tiresome to do this in every event that needs a 'face', but it looks OK.
Edit (Nov-7-2012): Another option: leaving a part of the textbox transparent and fitting the image exactly inside of that hole.