Hi there deadstroke, if what you are looking to post is the picture under your posting name to the left of the screen, I think this is what you are talking about?
It is a simple thing to do, once you have the image you want to use go to the "User CP" section of the board, the button for this is right next to the AZBillards title at the top there. Under that lick the "Edit Options" link, scroll down and you will see a section for editing your avatar. If I am right you can upload the image right from your computer, and not need to host it yourself. Keep in mind that the image needs to meet the guidelines set for the board, I think here it is 110px x 110px, not sure what the actual file size is set at though. As for file types... I know that *.bmp files are evil evil evil for web use, *.jpg or *.gif files are the best imo to use, again, this will depend on what file type the board is set up to utilize.
Hope that helps?