It seems your question about what Video Card type you have is still not answered.
Well, where do you plug in your monitor(Its that big square box where pretty images come up)? Do you plug it in where the PCi Slots are near or do you plug it in near where you plug in your Keyboard/Mouse. If it is near the PCI slots its AGP, if its near the Keyboard/Mouse its integrated graphics meaning you have to buy a PCI video card (the one you posted). There is no good video card that is PCI, your computer will never be a gaming computer, the best game you can play on that peice of junk is probably Pac Man with the graphics turned down way low *sarcasm(just a lil bit)*
I'm sorry for acting like a jerk and treating you like an idiot, but seriously, in this situation, you are kind of the idiot.
First off buying a retail computer for reasons other than Business/Serious Designing (like Apple or Sun Microsystem) is pretty stupid to begin with. If you find yourself stumbling upon a forum such as this one, you have an oppurtunity to have equal or higher knowledge of computers than anyone who posts here, you just need to pay close attention, and if that fails, ask a friend to build it for you.
Also you should have discovered the problem earlier, if I had warranty or whatever kind of service that has to do with the Best Buy, I'd haul the thing back whether its 10 minutes away or 3 hours away, and demand a refund or replacement. This is not even something that can be "forgiven," you deserve what you paid for (pretty little actually, but still money) and you should get it.
DOWN WITH STORE-BOUGHT COMPUTERS!!!!
Ok I'm done...