|"I should have been more specific"|
Please post the model number of your eMachines.
"I think the chipset is MCP61"
The nForce4xx chipsets were released in 2006 so it's unlikely there were ever any Win98 drivers. I'm guessing some sort of generic Windows driver installed automatically. The audio chip is probably not from NVidia. Look over the board & see if you can find the chip. It will be small, black, & located at the end of the PCI slots relatively close to the audio ports. Probably Realtek. Get the model number & then check the Realtek site for AC'97 drivers, not HD.