It's extremely rare that you can replace a GPU on a laptop. Most laptop GPU are part of the motherboard. From time to time, you might have some laptop where there is a mini PCI slot where you can put in a GPU. However trying to find a suitable GPU by itself is going to be extremely hard to impossible. If you want a gaming laptop, get one with a good video chipset in the first place.
As for sound, I do not that Creative Labs have released USB, PCMCIA and Express Card Sound Cards. Problem is that it does mean that you have a this seperate card or some ports that are going to be sticking outside of the laptop.
Moving thread to Laptop Section.