I have to admit, I hate these PCI graphic card discussions. So complicated, due to the dual monitor support.
Here's the official word on installing:http://www.dexplor.com/phpBB2/viewtopic.php?f=13&t=7747606
You might uninstall every video driver in sight, and shut down. Then disconnect the hard drive. Then go into the bios of what I think is a Intel 915 chipset, and set primary graphics adapter to PCI. AGP is onboard, I believe.
Then save changes and shutdown with CTRL-ALT -DEL. Then add the PCI card with power unplugged. If you can get the bios displaying on the new PCI card, shutdown and disconnect power. Reconnect hard drive and hope you just need to add the cards driver. I know that sounds very complicated.
But it might be simpler to reinstall Windows, and take it from the top. Thing is this is very difficult with eMachines restore disks. It's simpler with a retail install. With a retail install, you just omit the onboard graphics driver.