The compaq presario cq56 is a laptop. You cannot upgrade the video card.
Is it possible to add more memory to it? I know the accelerator is a Intel(R) 4 series express chipset family, but would I be able to have a decent gaming performance if it is improved to its max capabilities?
You can add more RAM to your laptop. I think the max is 2GB for older laptops and 4GB for current laptops.
Laptops generally have only two RAM slots; one on the underside of your laptop and one under the keyboard which means you need to partially take the laptop apart to access the 2nd slot. Assuming the max for your laptop is 2GB, you need to insert two 1GB RAM modules.
However, Intel's IGP is pretty weak and beyond a certain point no amount of dedicated RAM will increase performance because the IGP is too slow to access it. I'm guessing at best it might be able to effectively use 512MB of RAM for gaming. But Intel's IGP is not meant for gaming, so any gains may be marginal at best; like no more than a 5% improvement on the high end.
Unfortunately it is true that it is nigh on impossible to upgrade the graphics card in a laptop without some serious soldering and knowing EXACTLY what the hell you are doing. But one thing that I feel I should point out: my Laptop is a pretty sucky low end model but I can still upgrade the ram to 8 gb with Windows 7 OS.