Pick what you want for an avatar.

Resize it to 150x150 max.

Upload it to a host like imageshack.us or tinypic.com. Copy the URL they provide as a DIRECT link to the image.

Go here: http://www.scrapyardknives.com/ubbthreads/editbasic.php?Cat=
Paste the direct link to the image in the "URL to your avatar (150x150 max pixels, may be smaller) (.gif, .jpg, .png accepted)" field.

Save! <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /><img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" />