In what format is the file that you downloaded from DriverGuide? If it's a zip file, you'll have to unzip the file first so that the files inside are accessible. When the file is unzipped, look inside the unzipped folder, you might then see a Setup.exe file, if you do see it, double-click it to install the drivers. Alternatively, when the file has been unzipped, use the Add New Hardware Wizard again but this time point it to the unzipped folder as the place to look for the driver files.
To unzip the downloaded file, right-click on it and choose the "Extract All" option. It will, by default, unzip to the same folder that contains the zipped file.