This model is not listed on the Gigabyte website(s). That's a strong indication that it's an OEM motherboard. The closest match I was able to find is a GA-8I845GVM-775
If it's an OEM motherboard, then you will need to visit the pc makers website for support as Asus doesn't normally provide support for OEM boards.
This is the FTP link for Socket 478 motherboards but I wasn't able to find much there.
It's very possible the GA-8I845GVM-775
drivers will work on the GA-8I845GVM-RZ
. However, there are no Win 7 drivers posted, only Windows XP 32/64 bit drivers are available for this model.