Video card

A pci-e 2.0 card will work fine in a PCI-E 1.x slot, they are 100% backwards and forwards compatible. You also dont need to match the memory on your motherboard to the memory on the graphics card. You can use one with DDR2, DDR3, GDDR3, GDDR4, or even GDDR5 all of them will work just fine.

Are you gaming? If so at what resolution and please post the name and model number of your PSU so we can make sure it will power the card.

If you arent gaming, consider something like an ATI 4650, it should be more than sufficient for your needs and is relatively cheap.

Well i'm gaming but not too hardcore, just play WoW or CoD, something simple. I play at 1440x900 widescreen. Also I dont have my PSU yet im just willing to pay for one that is around 80-100 along with a gpu around 80-100

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$200 total before $20 MIR, it will allow you to play almost all games at high at that resolution.

both of those would work in
http://www.bestbuy.com/site/HP+-+Pavilion+Desktop+with+...
?