A texture is a texture, and when stored in VRAM it is the same size, regardless of the resolution you are playing at. Now you're right about not being able to play at high quality settings, but that has more to do with the actual processing power of the GPU than the VRAM.
It will indeed make a difference if a game can only fit 60% of the required textures into 256mb of vram. Itll thrash between system ram and vram.
I know the 330m is comparable to the 9600gt. Lets have a look. I couldn't find any at 1440x900 but here are some various resolutions. See how on certain games the 512mb version performs better in benchmarks.
...And by the way, I'm not sure how it read to you, but I was trying to emphasize that most modern games could be ran at medium settings on the non high-res screen. I didn't really mean that a 330m could run crysis or Bad Company 2 at high/ultra ;-)