Hi, Yuii:
Try this...
Download the drivers from this link below (second file listed 64 bit).
Extract the files onto a usb flash drive.
With the flash drive and W7 installation media plugged into the machine, boot from the W7 installation media.
After you select the install now option, select the Drive Options - Advanced menu, then select the Load Driver option.
You should now see the storage driver files listed.
If you check the box, it will only include the compatible driver.
Follow the prompts and hopefully W7 should install.