someone PMed me asking how to do it so i figured i would just copy and paste it here
avatar needs to be 80*80 pixels (but they will let you use higher or lower), make sure it is to scale (both numbers dividable by 8)
and something like 100k (but again you can use higher)
1. first upload your pic somewhere, i recommend imageshack (http://imageshack.us/)
2. go to the "my home" section of the forums
3. then go to "Personal information, email, password, etc."
put in the address of the place you uploaded your picture to making sure you select the "URL to your avatar (80x80 max pixels, may be smaller) (.gif, .jpg, .png accepted)" option
4. click submit
5. if you are like me and for some reason it doesn't work just wait a few mins for the page to time out and click refresh (F5)