Send it to the site administrator http://www.gl1800riders.com/forums/viewtopic.php?t=1306
or if your picture is no wider than 120 pixels in the jpg format and posted on the internet somewhere you can just put the link to it in the avatar control panel at the bottom of your profile. Check out the "support and testing board" for additional info on how to do stuff on this board.
Once you make your gallery and have the picture you want to use in it, use the thumb of your picture for your avatar. Right click on the thumbnail and select properties. Copy the url address from there and paste it in the avatar box.
If your more confused now, let me know and I, or someone will try to help you further.