Realtek drivers have a habit of leaving bits behind when an install goes wrong so I'd suggest you start out with Driver Sweeper to tidy things up: click here
Then download the latest drivers from the Realtek website (I think you have a HD rather than plain AC97 chipset): click here
Do not let Windows install anything but run setup from the driver package. It may then work directly or you may have to reboot and let windows 'find' the drivers that Realtek setup just tried to install.
What is on the ASUS website is fairly old - if these drivers worked with Vista they're really unlikely to work with SP1 !
Good luck, JimF