Sorry for the long wait.
That card looks good. The slot the computer has is PCIe x16 2.0. I don't really care if the card runs on half performance, I just want one that works and is better than the "directly attached to the motherboard" thing.
My max spending is $50. I don't think its necessary to get anything that can run Half life at 300 fps.
Being said that it now has 3GB and a decent card, I think it will be just fine for Blockland (minecraft too maybe).
Last thing: should the card be low profile (no fan), or should it have a fan? The noise doesn't matter since the case fan rattles loudly anyways.