To reduce use of harddisk space and the amount of moved data I'd like to have a hack which does the following thing:

People have to give up an URL for there avatar where the picture IS, so most of the time that will be a link to there own server space.. the avatar has to be loaded from that place, so it doesn't goes to the webserver..

i already made a custom user template for the avatar, and i used that in combination with an <img href="$customfield5" height="60" width="60" border="1"!> or something like that :)
but when someone doesnt fills in an avatar, you get a red cross, now how do i avoid THAT!

How about you create an avatar called none, which is a small transparant gif, you then set it so that the none avatar is the default this would solve the red cross problem