This might be considered a pointless post, but i just want to give some hope to those people who don't meet the system requirements.
I have a very old pc.
AMD athlon 64 3800+
2 Gig ram
Nvidea geforce 6500 gt -512mb (My display drivers date back to 2010)
After the 'dont meet system requirements' screen pops up i just left everything. I didnt click on anything, the installer just said 0%, but i could hear the disk spinning. The diablo3.temp folder was getting bigger. (this was all posted in these forums)
When the install finished (disk stopped spinning and shortcut was created) i ran the updater and played the game. Perfectly. It's actually running at medium to high settings without a glitch.
I cant speak for all the other errors that people are getting, but dont be deterred by the 'dont meet system requirement' message. Just leave it be and let it at least finish the install. If it works on my crappy pc then i'm sure it will work on a lot other people's systems as well.
good luck guys!