Hi,
I just got Enlightenment working today myself, using the CVS sources. I've not tried a jpg or png background, but used the ones from
www.get-e.org ,there's even an animated background!
You need to use the syntax: enlightenment_remote -desktop-bg-add 0 0 0 0 /root/e17_bg_sunbeams.edj
Hope this helps, I'll have a play around with e17setroot tomorrow and keep you informed,
Andy