First, are you sure that the problem lies in the driver? I've seen an awful lot of driver questions for which the driver was not the answer.
Second, which driver you need depends on your motherboard and the network chip on it. What model of computer or, if you built it yourself, motherboard do you have? The drivers should be available on their site, or on a CD that came with your computer or motherboard.
Third, has this never worked or did it work before? What happened just before it stopped working? Did you re-install the OS? Install a new OS? Knowing what caused it to stop working can help us identify the fix.