its called an avatar..

and go to a place like www.imageshack.us and load up a pic, where it has "file size" you can choose 640 x 480 pixels etc... and one of them will say "avatar 100 x 75 pixels" choose that one, then upload ur pic. Then when its uploaded copy the link from the "direct link" box, and paste it into ur "avatar" options on this forum.

as for posting images of ur car here for us to view, same process, but change the size of the image to suit a 17" screen or something. there is a thread on how to do it in the introduction section i think.