C-Media makes the chipset, AC97 is the audio standard it
follows, but these two alone are not enough detail to get a
driver that applies, except by random luck.
First, identify the device this audio chipset is on, is it a
sound card, USB dongle, motherboard, or???
Go to the respective maufacturer of that device, or get out
the spec sheet or a magnifying glass and write down the
c-Media chipset number, something like "CM-8738" for
example, and then you might find it on C-Media's website
http://www.cmedia.com.tw/EN/DownloadCenter_Detail.aspx?pserno=0&dtype=ALL
or might be able to use their 'site Search feature to find
it, or might then input that chipset number into a web
search engine.
Alternatively, if it shows up at all in Device Manager for
windows you can go into it's properties and on one of the
tabs it lists a Dev & Subsys ID string, which you can use to
identify the audio chipset and proceed with a web search for
it.
The easiest way is ususally to go to the product
manufacturer first, though the newest drivers tend to come
from the chipset manufacturer (C-Media). If all else fails,
MS' website may have it, but C-Media is pretty popular and
using above advice you should find the appropriate driver
for whichever OS you need it for... pretty important detail
you failed to mention...