As jk07 said, you needed to put the name of the driver, not the name of the video card itself. If you can edit/recreate your xorg.conf file, it should look something like this:
Identifier "Configured Video Device"
Identifier "Configured Monitor"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
Now, you said that this had no effect. As far as I know, this should be the way to get your video card working. I checked in my Synaptic Package Manager, and the xserver-xorg-video-openchrome package is already installed by default. This means that it should already be installed on your machine as well. So directing the xorg to use the "openchrome" driver should
get your 3D acceleration turned on. Curiouser and curiouser...
On another note, did you ever get a chance to launch the "Additional Drivers" application to see if there are any proprietary (i.e., not open) drivers available? It should be in your Mint Menu under "Preferences". If you can't find it, you can also launch it using the "Run Command" (press Alt+F2) and typing in "jockey-gtk" without quotes. Hit ENTER, and the "Additional Drivers" application should launch. See if there are any drivers there that you can activate.