My computer is a windows XP.
I was following "Getting Started with Arduino on Windows" and was up to "4 / Install the drivers".
I opened device manager>hardware update wizard and started to install the zipped driver that I downloaded off this site. It came up with "The software you are installing for this hardware: arduino uno, has not passed Windows logo testing to verify it's compatibility" so I clicked "Stop installation" but it came up with "Cannot install this hardware; an error occured during the installation of the device; the certificate is not valid for the requested usage".