Well, it is pretty easy. You need to download Upload Image Changer - http://www.zindasgoldensims.com/
I found a pretty good guide by FuryRed that I used when I first got it. You can find that here - http://furyredsays.blogspot.com/2010/01/how-to-get-custom-avatar-pic.html
I don't think it works on Macbooks, so I'm sorry if you have a Macbook. I've downloaded it, (obviously) and there aren't any viruses or payments. Just the download.
I found a pretty good guide by FuryRed that I used when I first got it. You can find that here - http://furyredsays.blogspot.com/2010/01/how-to-get-custom-avatar-pic.html
I don't think it works on Macbooks, so I'm sorry if you have a Macbook. I've downloaded it, (obviously) and there aren't any viruses or payments. Just the download.