You accidently get a shared memory video card by chance? Can't be sure just looking at the type of card. There are 8400 GS with entirely discrete memory and 8400 GS with mixed memory.
Oh and make sure your laptop specific type things are inline. Like high performance options. Laptops have throttles.
You consider driver updates? There is a site that hacks nvidia desktop drivers into laptop drivers. I forget the name or I would post it.
Edit: this site http://www.laptopvideo2go.com/
Technically speaking every laptop manufacturer is supposed to release its own graphics card ini (technically called a driver). Some companies even major ones have bigger issues with this than others.
I have a dell and I used that site for a little gain back when I bought it.
Consider using a standard benchmark like 3dmark 05 so we can all relate.