I tried. I just took a url for a picture that I found on a website and put it in the box; and then specified my pixels at 100X100 and I couldn't get it to work. Do I have to load it to a picture hosting site or something?
Yes, you need to load it to someplace like tinypic. It needs to be less than 100x100 and I had to hit enter rather than "modify profile" for it to work for me.
tinypic is easiest. Just c&p the url and you can change it over to tinypic that way. Click on avatar (from the drop box) and it will resize it smaller for you.