When starting a clean installation with the newest umbraco build and setting read/write permissions it still didn't work. Turns out there was an error in the web.config file at line 171. I uncommented the ASPNETAJAX section and then I could start the installation.
But then I kept getting a "database initialisation failed". Turns out i had to manually add the connection string and refresh the page. Oh yeah, and don't use dots in your password / login name or database name, ms sql really doen't like that.