Video Cards. Please Help!?

I need to know how to choose a video card.

I've got the video card integrated with my Dell Dimension 3000 and quite frankly, its useless!

I've been looking at some more updated video cards, but then I don't know what kind of socket I need or have. I've checked the specs on my motherboard and it says I have a PCI-Express video card socket, so should I be looking for a PCIe Video Card?

And in terms of their memory jargon, my computer supports DDR2, and many of these cards are DDR3, does it matter when it's video cards?|||Your motherboard doesn't have a slot for a graphics card to be installed into, you are stuck with the integrated graphics you have... It is time for a new system...

As for graphics ram, you can use any graphics ram in a system you want to. The system ram is totally a separate category...