1. Those CPU's have built in graphics which is much like the onboard graphics available on many motherboards.. Its basically usefull only for folks who use their PC for office work.. You surely can install your own video card provided the motherboard has the appropriate slot for it and your PSU has enough power to run the card.. Rest assured, the inbuilt graphics chip in the CPU's wont interfere with your graphich card..
2. RAM support depends on the motherboard.. However, most of the newer motherboard(s) feature DDR3 RAM slots and thus you wont be able to use DDR2 RAM..
3. Yes.. The integrated sound chip is present on every motherboard..
ohk thnx buddy.. just one more thing, is the integrated soundchip good or i may have to install it sEparately may be creative sound blaster or somthing coz am having creative 5.1 72rms speakers.