Ok, if you possess a .tar file then you will need to do the following.
tar -zxvf filename
cd "to the new directory"
READ THE INSTALL OR README SECTION (this will be located within the new directory created) because there are a lot of drivers written that do not follow the conventional steps for installing a .tar file.
(You need to be root for the make install process.)
Make sure to read the instructions regarding the installation of this driver. You might want to check out the linksys website for more information.
Other sources to check for installation instructions are:
your distros website