You should look for a graphics card with PCIe X 16 connection.
You can use ATI's 16XX or 19XX series or Nvidia 84XX or 76XX/79XX series, all of these are not state of the art but they're adequate to your description, take a card with at lest 256MB memory.
Look for a card with an S-video out put or a RCA output (video output).
As to specific model and prices you should see in you region what is available.
