Wat is the difference between ddr3 and ddr and wat are they coz i dont have an idea and also wat is gpu?

I know they are all stuffs to do with video cards,i am saying tis because i need a video to buy so i can play games of nfs carbon getting up(which says it needs a video card dat support shaders i need you to help me buy the right one:and plz it has to be invidia heres mi p.c info pc name:dell dimension 3100 card name: intel(r) 82915g/gv/910gl express chipset family operating system: windows xp home edition (5.1, build 2600) service pack 2 memory: 512mb ram processor: intel(r) pentium(r) 4 cpu 2.80ghz (2 cpus) display memory: 128.0 mb and plz tll mi de cheap 1 if available and wat iz cpu
Answer
Hi ddr and ddr3 are different sizes of ram (random acsess memory) so if you want to expand your pcs ram you can usually find the size (or name) of it on the ram in your pc. gpu is a global processing unit, it helps to transmit data. a cpu is a centeral processing unit. you can usually get nice deals on pc stuff at www.misco.co.uk or at www.maplins.co.uk