Here is the install guide from Arduino.cc website.
You need to go to the start menu (Win7) right click on computer and select properties.
Then select device manager upper left hand corner.
Select the USB device and right click - update driver .
Then window pops up w/ search automatically or manually browse.
Select manually browse.After that it will show you the path pointing to the driver - select browse (to the right).
Select the path to where Arduino software was installed.
You cannot install drivers from the download file folder. Maybe check program files directory?
You may need to uninstall, and re install directly to the C:\ drive.
Then the drivers would be located at C:\arduino-1.0.3\drivers
That little black caterpillar you just stepped on will set you back a few bucks....