Ive just purchased a new graphics card MSI ddr2 512mb and it doesnt fit my P4 that runs DDR400 ram. My question is if I change graphics card to DDR1 will That card work in new board that supports ddr2. I have a new mobo and am slowly building new pc but need graphics for old pc games and dont want to buy 2 graphics cards.( will graphics card from old pc work on mobo that supports dual core ang core 2 duo?
DDR based graphic cards will work in DDR2 motherboard, DDR2 in DDR3, GDDR5 in DDR3, simply because the graphic card's memory controller is separate to the motherboards' memory controller. The reason why it did not fit was most likely because your P4 is using the AGP interface while you bought a PCI-E graphics card.
The old graphics card from the old pc will work if the graphic card is PCI-E and not AGP.