While replacing a power supply does not mean you replace the motherboard, CPU, RAM and all that it can extend the usable life of what you have and enable you adding your new 3D card.
Tell a little more about your PC. For instance any dual core is great for video work and if a celeron I'd want to move on to a new machine...
I have a Dell XPS 400 and I'm strongly into gaming and editing HD video. So I was on the market for a Nvidea 8800 GTS graphics card when I realized that the Dell XPS 400 has only a 375W power supply and this card requires at least 450W. So I ask my computer associate and he said that to buy a new power supply would mean something about a new processor or motherboard. SO HELP ME! is it right to upgrade or get a new computer?