I'm not sure if my experience is typical, but without using the workaround below I am unable to install from Win7 x64 even though User Account Control (UAC) is disabled, even if using the "run as administrator" option.

If I launch an upgrade or SP install, it pulls up the correct directory to install to, but if I attempt to proceed directly I receive an error:



However, once I click OK, and then actually browse through to that same directory, it seems to refresh the install and it will then accept that directory and install correctly.

It also seems that you only need to do this for the first upgrade/SP, as long as you don't reboot your computer between installs.