For anyone else reading this, you have to rename the .zip file to xfree.gz, then run gunzip on it. The resulting xfree file is a simple concatenation of the config and log files. Took me a bit to figure that out.
Anyway, you need to get rid of the ChipSet line in your Device section. The nVidia driver doesn't use that -- it can determine what chipset is being used just fine on its own.
While you're at it, comment out the BoardName line too. It's redundant (mostly for the same reason).