You can use your old card (unless you want to sell it with your old computer), and see how it works with the new CPU etc. The new cards can only get cheaper too. The latest video cards are 8X AGP so make sure the motherboard you get has an 8X AGP slot. The new MB also have serial ATA Hard drive interfaces and RAID controllers.
It's all sometime to much to keep up with.

Just do some google searchs for the components you are thinking of getting and there will be tons of hits.

+++"Nothing except a battle lost can be half as melancholy as a battle won."+++

The Duke of Wellington