A video card has it's own GPU and RAM, so it improves graphics by not hogging the onboard RAM and CPU so much.
Never head of a video chipset. If you mean the chipset on the motherboard, they are what let the manufacturers put certain things on the motherboard, like a LGA 775 socket, AM2 socket, 3 PCI-E slots, AGP slot, etc.
What's wrong with the computer?