- grab your copy of Image Ready (part of Photoshop) and create a new file (100x100 max).
- on one of the layers, put the text you want to scroll
- move the text to the very right, so you can't read it
- open the animation box (Windows Animation)
- press the new frame button and click on the new frame
- move the text to the very left, so you can't read it either
- press tween, enter 10 - 15 as a tweening value here.
you should get something like this which you can upload as an avatar
(some people might find that distracting, though)