This thread sounds familiar? Did you ask this question here before?
already said most of it, but to recapitulate:
- What midi interface are you using? If it's a generic USB-Midi cable: the driver (class compliant) is included in Windows 7, and will be installed automatically.
- Generic USB-Midi cable are not recommended with older synths. Buy a midi interface that has it's own driver, like a Midisport one, for example.
- The Yamaha driver is for a Yamaha Midi Interface, the AN1X itself doesn't have drivers, and doesn't need them.