I started my install last night and it sat at 0% installing for about 4 hours. I deleted all the folders associated with Diablo III, including the Battle.net folder in ProgramData, and started, stopped, and manually started the Agent.exe file (might have been Agent32.exe, I'm not staring at it right now). I also went into the Services and put the System Logon or whatever it was to Automatic from Manual. I even put it to disabled and applied settings, then put it back to Automatic to make sure it got a "fresh" start.
Am I missing something?