New answers tagged windows
In Settings -> Options -> System of QGIS, you will be able to see the read only current environment variables of your system; precisely the folder where your temporary data are being written (see next image). You can edit the path of these folders by using the Control Panel of Windows (filtering by env at the browser); see next image.
The two top answers by @SCW and @Mike Toews are great. The site listed by Mike is for unofficial binaries - which was very useful when 64 bit GDAL was not readily available (as per the time he wrote his reply), but it has been now for some time. I have added this alternative answer here as, although I have mentioned it many times, it still keep cropping up ...
I'm using a ms4w build http://www.maptools.org/ms4w/. It's quite enough for me, but it seems to be frozen. Also you can use OSGeo4w package http://trac.osgeo.org/osgeo4w/.
From my experience, there are 2 possibilities: Have you tried to format your computer? Have your tried to disable your anti-virus for the installation? In the company I work, 4 computers installed it with no problems, but other 2 had exactly the same issues you described (running on 64-bit Windows 7). We had to format these 2 computers, and after that ...
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