There is, not a lot of people know it though. I believe it is /opt autoupdate 0... Just type that and it shouldn't download anybody's textures....

Also, Omega.... For some people the download lag is not for just when it is downloading yourself. When I go ingame and some of my friends have their full 512 on, it will lag half way through the first turn frame. (on the netbook) That is why I had to take off my 512 some time ago, because it kept lagging me. (if you are in quick aikido, you miss the whole first frame)