do a google images search for an avatar u like, once u find one, right-click it & go to "Properties" the url is in there, just copy & paste the url into ur avatar box in ur profile & u'll be good to go, about the moving avatars, I'm not entirely sure how to get them, but I know that an image has to be saved as a .gif to be used as a moving avatar or sig, here is one I found if u want to use it, just copy & paste the address into ur avatar box:
http://users.netconnect.com.au/~ryley/a4alien.gif