hi
i have resolved your problem
sorry i m french so my english is no good....
i have the same computer vaio PCG GRT816M than you
just install the nvidia driver 6229 on nvidia site...
and modify your XF86Config file---->
section device
Identifier "device1"
Driver "nvidia"
Option "NvAGP" "1"
EndSection
that's all ....
it work good .
bye