First fix, if you are stuck on updating then you need to go to C:\Documents and Settings\All Users\Application Data and delete the battle.net forlder.
Once you get past that then you can install the game. Unfortunately, for XP users you may get stuck on 0 percent install and the game will not install.
To fix this I had to take an unconventional method but it worked for me. I basically had a laptop with windows 7 on it. I installed d3 there and then I took the C:\Programs\Diablo III folder and copied it to a portable hardrive. I then transferred the folder onto my server's c: drive into the programs folder and ran it.
I know this is not the greatest fix but it works perfectly. To blizzard coders. Why do we need to introduce coding which blocks people from installing on a legitimate OS. This code is extremely annoying as its only purpose is to prevent installation. If it installs and works then good. If it installs and does not work then darn. Please at the very least, let it install.