Q: Are there significant differences in quality between the GeForce 8400 GS and the 8800 in terms of high-end quality? And would it be worth taking my new laptop apart to replace it?
A: No can do. In laptops it's impossible. Only some really high-end beefed-up notebooks'll let you do it. More or less everything is built-in in standard ones. You can add RAM and try replacing CPU though - that'll give you some speed. Do some tweaking - I manage to play new games on old 6800 512MB. Write me if you need help.