Instead of giving you the fish, let me try to teach you fishing.
Here we go:
Write: mercury pi945gcm
Click on first result (http://www.mercury-pc.com/product-detail.php?link=p-mainboards&subtitle=Mainboard&productid=751)
Scroll down, there's a "Download Drivers" menu at the bottom. On that page, it says "Sound Driver" and the Download button.
It doesn't say if it is Windows 7 compatible, the Lan driver below says that it's Vista compatible, so there's a chance.
If it doesn't work, you have to look for the specifications, http://www.mercury-pc.com/product-spec.php?productid=751
it says this motherboard has an "IDT 92HD202 6-channel High Definition audio Codec", so you search with this on google.com.