I used to have it installed and working on this machine and removed my previous install using Add/Remove Programs.
However, now when I try to reinstall the game, the Diablo 3 Setup starts 'Updating setup files...' and then hangs; I have had a quick google for ideas on how to fix it which seems to bring up a bunch of posts when the server loads were really high last year, nevertheless I have been through the list of suggestions, making sure that secondary login is enabled, running the installer as administrator, etc.
I did some additional googling and found a post on a blue tracker which simply advises to perform all of the steps I have already run through.
For whatever reason, Internet Explorer (which I never use) was set to "work offline".
The PC is a Dell XPS L502X with a Core i5 2450M , 6GB of RAM, Nvidia GT540M GPU. It started , but for the past 2 hours it's been stuck at "Getting Setup files". Short answer: Disconnect the Internet connection and try again.