System Constantly Warns To Update

I am getting really frustrated with the Windows updates, have 3 computers, 1, the newest one, constantly warns me to update, the other 2 are older, but all of them XP with SP2 and somehow I managed to stop the bothersome popup. I am on dial-up, no one can call me, since MS constantly updates despite I unclick automatic updates. My Windows folder on the new computer is 3 GB and originally it was under 1 gigabyte. This computer is only 4 weeks old. So if nothing ever gets really fixed, why take up so much space? And why update? Where can I find out just how large the Windows directory should be? My other old laptop, where I reinstalled the original 6 year old version of XP and then from the disk Microsoft has sent me SP2, I did not update ever, It works just as fine.