aupad :
it is a new pc from walmart. It is a no name brand, pretty risky, i know. But every single review out of 60 was almost 5 stars. 16 gb ram, intel core i5 2320, 2tb harddrive.
Your overall plan seems good to me. The processor is Intel, so they cant really cut corners there! The power supply is where no-names usually cut corners - and you are replacing that.
You want to purchase your graphic card online -- because graphic card models change so quickly, no stores can really compete with newegg.com on prices and are often left selling older cards at high prices. If you outline your price range we can provide input on the card. You can also scan tom's "best graphics card for the money" articles which are very informative for a new buyer.
When purchasing a power supply don't get caught up focusing on getting the most wattage for the money. Many new buyers do, but it is actually the brand/manufacturer that matters most on this part -- because reliability is the #1 concern. You will notice that the brands I highlighted above typically have better and longer warranties than some other brands -- this is another sign that they take quality seriously. Also, FYI - Most graphic card manufacturers assume you have a lower quality power supply, so they recommend more wattage than is actually necessary in order to insure a large safety margin. A brand-name, high quality 500w power supply can run almost any card with no problem. Higher wattage is intended for overclocking and multiple power supplies.