Please only buy at best buy if they have a sale.
Go to newegg and get the best card you can afford.
My friend just bought this card and he loves it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150359
But there are many others as well. I am a Nvidia man but ATI/AMD makes some great cards.
The memory does not matter as much as the actual card processors.
The 8800 GTX is a faster card than the 9500 no matter the VRAM size.
I'm a noob at this. How will I know which cards are better? I'm looking for something in the $100 range i think. If I get a $200 card, I might as well get the 15 inch macbook pro, will my upgraded pc be that much faster then the macbook pro 15 middle?